JPH0495843A - Prediction of breakage of optical fiber - Google Patents

Abstract

PURPOSE:To enable appropriate prediction of breakage of an optical fiber by performing a strength test of an optical fiber of the same kind as a fiber to be measured and specifying a reference relation between a breakage rate and a strain of said fiber. CONSTITUTION:First, a strength test of an optical fiber of the same kind as a fiber to the measured is performed to specify a reference relation between a breakage rate and a strain of said fiber. Then pulse light beams having differ ent wavelengths emitted from light pulse testers 6,7 are incident to the optical fiber 3 to be measured via a light switch 5a. Further, Rayleigh-scattered light from the optical fiber 3 is received by the testers 6,7 again via the light switch 5a, and a light transmission loss of the optical fiber 3 is remotely measured per wavelength of the pulse light. The measurement results are sent to a data analyzer 11, where a bend diameter and bend length of a bend strain applied to the optical fiber 3 are separated from each other to be detected. Then from the measured strain amount and the reference relation, a breakage rate of the optical fiber to be measured is calculated based on a relational equation.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for predicting breakage of optical fibers constituting wired transmission lines and the like.

(Prior art) In recent years, optical fibers have been widely used as transmission media for wired transmission lines because they have the characteristics of large capacity and low loss. However, optical fibers are made of quartz glass. Since it is a brittle material such as, if long-term quantum is applied, it will break due to static fatigue phenomenon and optical signals will no longer be transmitted.

Fractures due to static fatigue occur suddenly without any signs of changes in transmission characteristics, and since optical fibers have a large transmission capacity, such unexpected fractures seriously impede the operation of communication networks.

Here, the knowledge that has been revealed so far regarding the static fatigue rupture phenomenon of optical fibers will be described below.

The static fatigue fracture phenomenon of optical fibers is explained by the brittle fracture theory of glass.

According to the brittle fracture theory, minute scratches on the glass surface gradually grow in the presence of stress and eventually break. The time t until rupture is determined by the following formula (1), where the applied strain is 51, the size of the initial scratch on the glass surface is X, and A and n are constants (Reference Literature: Journal of the Institute of Electronics and Communication Engineers J66-8.7
．． p82B-829 "Optical fiber strength assurance method by screening test").

i=AX-(n2)/2s-・,,
(1) Therefore, in order to predict the rupture time t of an optical fiber, the size of the flaw X and the size of the applied strain S (
or the magnitude of the stress proportional to the stress S).

However, in reality, the flaw size X is usually less than 1 μm, and it is almost impossible to grasp the size of such flaws over the entire length of the optical fiber that makes up the transmission line. be.

Conventionally, a method has been proposed in which a test sample is extracted from optical fibers manufactured under the same manufacturing conditions and a strength test is conducted to statistically determine the size of the flaw. If the size of the flaw can be ascertained in this way, as long as the applied strain S is known, the optical fiber will break within a certain time t, even if the break time t itself cannot be predicted. It becomes possible to calculate the probability (hereinafter referred to as rupture rate) p.

This rupture rate p is given by the following equation (2), where n, m, and k are parameters representing the flaw distribution and flaw growth rate determined from the strength test of the test sample.

In(p)・(m/(n-2))l+(m・n/(n-
2)) In(s)+k...(2) In order to reduce the breakage rate p of the optical fiber, a certain amount of strain is applied for a short period of time immediately after the optical fiber is manufactured, and the scratches on the surface of the optical fiber are removed. A relatively large portion may be removed before use. In this case, the rupture rate p is also determined by the parameters n, m, N, representing the distribution of flaws and the growth rate of flaws obtained from the strength test of the test sample, , strain 81 time t, amount of strain S3 applied immediately after manufacturing, and strain application time. As a function of t, the following (3
) is given by the formula.

In(p)In(n+/(n-2)) +In(N, )+n1n(s/s, )+In(f
/ip) - (3) (Means for solving the problem) However, the methods that have been proposed so far for predicting breaks in wired transmission lines using optical fibers have only focused on the optical transmission loss of optical fibers. It is only a device that can judge and predict failures of optical fibers only by measuring them (References: Japanese Patent Publication No. 2-20049 "Optical Fiber Cable Breakage Prediction Device", 1990 Spring National Conference of the Institute of Electronics, Information and Communication Engineers, B -888 “Configuration method of optical line testing and management system”).

Such breakage prediction methods are effective to some extent in determining and predicting failures due to an increase in optical transmission loss in optical fibers, and in determining failures due to optical fiber breakage. This is caused by the strain applied to the optical fiber, and since the magnitude of this strain cannot be directly determined by measuring the optical transmission characteristics of the optical fiber, it is useful for predicting optical fiber breakage failures. do not have.

To be more specific, there are two types of strain that can be applied to an optical fiber: elongation strain and bending strain.However, no matter how much elongation strain is added, the optical transmission loss will not increase at all, so conventional fracture prediction methods cannot , it is completely impossible to measure this type of strain, and it is completely impossible to predict the subsequent breakage of the optical fiber.

Furthermore, when bending strain is applied, the optical transmission loss of an optical fiber increases, but the amount of increase in loss is not only due to the magnitude of bending strain;
It greatly depends on the bending length and the structure of the optical fiber to which the bending is applied, such as the core diameter and refractive index distribution.

Therefore, special measures are required to calculate the magnitude of bending strain from the measurement results of optical transmission loss, but inspection systems based on conventional methods do not take any measures to prevent bending. It is impossible to calculate the strain or predict the subsequent breakage of the optical fiber.

One of the reasons why conventional methods have not been used to predict fracture is that of the two types of strain mentioned above, only a method for measuring elongation strain has been developed so far (References :
0ptical Fiber Communicati
.

n conference 90. PD-15”
First measurement of str.
ain along field-installed
optical fiber brill
ouin 5pectroscopy), a method for measuring bending strain has not yet been developed. This is because the total strain applied to the optical fiber cannot be calculated.
Another reason is that a method for predicting breakage of an optical fiber when strain cannot be measured has not yet been developed.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical fiber breakage prediction method that can accurately predict the breakage of an optical fiber.

(Means for Solving the Problem) In order to achieve the above object, in claim (1), a strength test is performed on an optical fiber of the same type as the optical fiber to be measured, and a standard for the fracture rate and strain of the optical fiber is determined. The relationship is defined, light of a predetermined wavelength is propagated through the optical fiber to be measured, this propagated light is detected, the amount of strain in the optical fiber to be measured is measured, and the amount of strain is determined from the measured amount of strain and the reference relationship. The breakage rate of the optical fiber to be measured is calculated.

Further, according to claim (2), a strength test is performed on an optical fiber of the same type as the optical fiber to be measured, and a reference relationship between the fracture rate and strain of the optical fiber is defined, and the optical fiber to be measured is An optical fiber of the same kind as the optical fiber to be measured is installed under the same conditions as the optical fiber to be measured, and the breakage rate of the same kind of optical fiber from the time of installation to the present time is measured. Calculate the amount of distortion,
The future breakage rate of the optical fiber to be measured is calculated from the calculated strain amount and the reference relationship.

Further, according to claim (3), a strength test is performed on an optical fiber of the same type as the optical fiber to be measured, and a reference relationship between the fracture rate and strain of the optical fiber is defined, and the optical fiber to be measured is Light of a predetermined wavelength is propagated through the optical fiber, and this propagated light is detected to measure the amount of strain in the optical fiber to be measured.In addition, an optical fiber of the same type as the optical fiber to be measured is installed under the same conditions as the optical fiber to be measured. Then, measure the breakage rate of the same kind of optical fiber from the time of installation to the present time, calculate the amount of strain of the same kind of optical fiber from the measured breakage rate and the reference relationship, An estimated amount of strain is calculated from the amount of strain, and a future breakage rate of the optical fiber to be measured is calculated from this estimated amount of strain and the reference relationship.

(Function) According to claim (1), a strength test is performed on an optical fiber of the same type as the optical fiber to be measured, and a reference relationship between the fracture rate and strain of the optical fiber is defined.

Here, light of a predetermined wavelength is incident on the optical fiber to be measured and propagated. This propagating light is detected by a light receiver,
Based on this detection result, the amount of strain in the optical fiber to be measured is measured.

Next, the breakage rate of the optical fiber to be measured is calculated from the measured strain amount and a predetermined reference relationship, and a breakage prediction of the optical fiber is performed based on this calculation result.

According to claim (2), a strength test is performed on an optical fiber of the same type as the optical fiber to be measured, and a reference relationship between the fracture rate and strain of the optical fiber is defined.

Next, an optical fiber of the same type as the optical fiber to be measured is installed under the same conditions as the optical fiber to be measured, and the breakage rate of the optical fiber of the same type from the time of installation to the present time is measured.

Next, the amount of strain in the same type of optical fiber is calculated from the measured fracture rate and a predetermined reference relationship.

Subsequently, a future breakage rate of the optical fiber to be measured is calculated from the calculated strain amount and the reference relationship, and a breakage prediction of the optical fiber is performed based on this calculation result.

According to claim (3), a strength test is performed on an optical fiber of the same type as the optical fiber to be measured, and a reference relationship between the fracture rate and strain of the optical fiber is defined.

Here, light of a predetermined wavelength is incident on the optical fiber to be measured and propagated. This propagating light is detected by a light receiver,
Based on this detection result, the amount of strain in the optical fiber to be measured is measured.

Further, an optical fiber of the same type as the optical fiber to be measured is installed under the same conditions as the optical fiber to be measured, and the breakage rate of the same type of optical fiber from the time of installation to the present time is measured.

Next, the amount of strain in the same type of optical fiber is calculated from the measured fracture rate and a predetermined reference relationship.

Next, an estimated amount of strain is calculated from the calculated amount of strain and the measured amount of strain, and a future breakage rate of the optical fiber to be measured is calculated from the calculated estimated amount of strain and the reference relationship, and this calculation result is Based on this, prediction of optical fiber breakage is performed.

(Example) FIG. 1 is a configuration diagram showing an example of a measurement system used in the present invention. In FIG. 1, 1 is a main signal transmitter, 2 is a main signal receiver, 3 is a plurality of optical fibers to be measured,
4a, 4b, and 4c are optical branching devices, 5a, 5b, and 5c are optical switches, and 6.7 is a well-known optical pulse tester, which have different measurement wavelengths. 8 is a pulsed light generator, 9
1 is a light receiving device, 10 is a wavelength sweeping type light source, 11 is a data analysis device, and 12 is a database including a magnetic disk storage device and the like. Note that among the wiring shown in FIG. 1, solid lines indicate optical wiring, and broken lines indicate electrical wiring.

Since each optical fiber 3 is normally connected to a main signal transmitter 1 and a receiver 2, the measurement system used in this embodiment includes an optical branching device 4a, It is connected to each optical fiber 3 via 4b. Further, optical switches 5a, 5b, and 5c are used to select each optical fiber 3 to be actually measured and to select a measuring device.

Next, the procedure and principle of the method of the present invention using the measurement system configured as described above will be explained step by step.

First, a method for measuring bending strain will be explained.

To measure bending strain, pulsed lights with different wavelengths emitted from the optical pulse testers 6 and 7 are appropriately selected by the optical switch 5c, and are made to enter the optical fiber 3 to be measured via the optical switch 5a. . Furthermore, the Rayleigh scattered light from the optical fiber 3 is again appropriately switched by the optical switch 5c via the optical switch 5a, and is received by the optical pulse tester 6 or the optical pulse tester 7. The amount of optical transmission loss in the fiber 3 is measured remotely.

These measurement results are sent from the optical pulse testers 6 and 7 to the data analysis device 11, where predetermined data processing is performed to determine the bending diameter and bending strain of the optical fiber 3. Detected separated by length.

Here, the number of optical pulse testers 6.7 is not limited to two, and can be increased according to the number of measurement wavelengths of pulsed light required for data processing in the data analysis device 11. Alternatively, a single optical pulse tester may be provided with a plurality of pulse light sources and share a display section, an operation section, etc. Further, the optical transmission loss amount may be measured by installing, for example, a semiconductor laser and an optical power meter at both ends of the optical fiber 3 to be measured, without using the optical pulse testers 6 and 7. However, even when there are two or more curved portions, there is an advantage in that the amount of optical transmission loss at each curved portion can be measured separately if measurements are performed using the optical pulse testers 6 and 7.

As mentioned above, in order to detect bending strain (bending diameter, bending length) from multiple optical transmission losses measured using pulsed light of multiple wavelengths, it is necessary to Using an optical fiber of the same type as the fiber 3 and an optical pulse tester of the same type as the first pulse testers 6 and 7, the relationship between the amount of optical transmission loss due to bending strain and the bending diameter is determined, and the data analysis device 11 uses the data as reference data. It is necessary to memorize it.

That is, when an optical fiber is bent, the amount of optical transmission loss of this optical fiber increases, so bending strain can be detected by measuring the amount of optical transmission loss of the optical fiber to be measured. However, this amount of optical transmission loss does not increase even if the bending strain applied to the optical fiber increases, that is, even if the bending diameter decreases, or the length to which the bending strain is applied (hereinafter referred to as the bending length) increases. It will increase even if For this reason,
Even if the amount of optical transmission loss is measured using pulsed light of different wavelengths, it is impossible to detect the bending diameter and bending length separately.

In addition, by using an optical pulse tester to measure the amount of optical transmission loss, it is possible to identify the location where bending distortion occurs, but it is necessary to ensure the dynamic range necessary to measure the actual transmission path. In order to achieve this, the distance resolution of the optical pulse tester must normally be on the order of 10 m to 100 m, whereas the bending diameter of the bending strain that leads to breakage of the optical fiber is several mm to several (1). For this reason, with the distance resolution of the optical pulse tester, it is completely impossible to separate the bending diameter that leads to breakage of the optical fiber from the bending length and detect it.

Therefore, in this example, we take advantage of the fact that the influence of the bending diameter and bending length due to bending strain on the increase in optical transmission loss varies depending on the wavelength of light propagating through an optical fiber. By measuring the increase in optical transmission loss using light, the bending diameter and bending length are detected separately.

In this case, the relationship between the amount of increase in optical transmission loss due to bending strain of the optical fiber and the bending shape, that is, bending diameter and bending length, is as follows:
It varies depending on the type of optical fiber to be measured (for example, single mode optical fiber and multimode optical fiber are completely different, and even the same single mode optical fiber differs depending on how the refractive index distribution is given). It is necessary to understand in advance the relationship between the amount of increase in optical transmission loss due to bending and the bending shape using the same type of optical fiber.

Next, the present invention will be explained in detail by taking as an example a single mode optical fiber having a step-like refractive index distribution (hereinafter referred to as an 8M Sl type optical fiber).

It is well known that the relationship between the amount of optical transmission loss S due to bending strain and the bending shape of an 8M Sl type optical fiber is given by equation (4) (Reference: D. Marcus, "Cuva
true 1oss formula for opt
ical fibers”Applied 0ptic
s, 19,9. pp1493-1500).

Here, R is the bending radius, L is the bending length, b is the propagation constant in the axial direction of the optical fiber, k is the propagation constant in the core perpendicular to the axis, r is the propagation constant in the cladding perpendicular to the axis, K+1 ．． -, is a modified Bessel function, ■ is a normalized frequency, a is a core radius, and π is pi.

As shown in equation (4) above, the optical transmission loss amount S is determined by parameters related to the bending shape (hereinafter referred to as bending parameters) such as the bending diameter 21 and the bending length.
, V, and a, which define the transmission characteristics of the optical fiber (hereinafter referred to as transmission parameters). These transmission parameters can be determined by inspecting the optical fiber after it is manufactured. Therefore, the unknown parameters in equation (4) are the bending parameters bending radius R and bending length L.

What is important here is that since the transmission parameters change depending on the wavelength of the light propagating within the optical fiber, as can be inferred from equation (4) above, the optical transmission loss due to bending differs depending on the wavelength (hereinafter referred to as However, this wavelength dependence itself differs depending on the bending radius R. Therefore, by examining the wavelength dependence of loss, the bending radius R can be calculated. , As a result, the bending length L can also be calculated.The wavelength dependence of the loss mentioned above is
For example, this can be investigated by measuring the amount of optical transmission loss using pulsed light of a plurality of different wavelengths.

Note that in the above example, the wavelength dependence of loss is affected only by the bending radius R, but in optical fibers with different refractive index distribution shapes, the wavelength dependence of loss also depends on the bending length. Even in this case, the dependence is usually on the bending radius R.
Since the bending length L is different from the bending radius R, the bending radius R and the bending length can be calculated from the results of measuring the amount of increase in optical transmission loss using light of a plurality of different wavelengths.

In any case, if you know the transmission parameters, the unknown parameters in equation (4) are the bending radius R and the bending length, as mentioned above, so at least two different wavelengths can be used. By measuring the amount of optical transmission loss using light, the bending radius R and the bending length can be calculated. Of course, in order to reduce the influence of measurement errors that accompany measurements, the amount of optical transmission loss is measured using light of three or more different wavelengths, and from this measurement result, the bending radius R and bending length are calculated using the least squares method. L
may be calculated.

Next, as a more specific example, an example of a method for calculating the bending radius R and the bending length L of an Sl type 3M optical fiber will be described.

Figure 2 is a diagram showing the relationship between the ratio of optical transmission loss and the bending radius R in an SL type 3M optical fiber.
IuSM optical fiber (hereinafter referred to as optical fiber) and the same type of optical fiber (core diameter 9 μm, non-refractive index difference 0.32%)
) is the increase A in the optical transmission loss amount S due to bending when light with a wavelength of 1.65 μm is propagated, and the increase J in the optical transmission loss amount S due to bending when light with a wavelength 1.55 μm is propagated.
Curve C shows the dependence of the ratio to IB on the bending radius R.

This relationship was determined as follows.

That is, using an optical fiber of the same type as the optical fiber to be measured and an optical pulse tester of the same type as the optical pulse testers 6 and 7 that emit pulsed light with wavelengths of 1.65 μm and 1.55 μm, bending strain was applied. The amount of optical transmission loss Sla and Slb for each wavelength in the optical fiber in the non-contact state is measured.

Next, with a bending strain of a predetermined bending radius R applied to the optical fiber, optical transmission losses 82a and S corresponding to each wavelength are similarly applied.
Measure 2b. After this, the difference between these measurement results is calculated, and the amount of increase in optical transmission loss due to bending strain A for each wavelength is calculated.
(=82a-8la).

Find B (=S2b-3lb). Next, the ratio (A/B) of these increases A and B is calculated, and this ratio (A/B) is calculated.
B) and the bending radius R are correlated.

As a result, the ratio of the amount of optical transmission loss unrelated to the bending length L (
It is also clear from equation (4) above that the relationship between A/B) and the bending radius R can be determined.

The bending radius R of the optical fiber 3 to be measured can be easily detected by using the relationship between the optical transmission loss ratio (A/B) and the bending radius R obtained in this way as a reference relationship.

That is, pulsed light having a wavelength of 1.65 μm and a wavelength of 1.55 μm is propagated through the optical fiber 3 to be measured, and optical transmission losses 183a and S3b are measured for each wavelength. Next, from this measurement result, the amount of optical transmission loss Sla when the above-mentioned bending strain is not applied is determined.

By subtracting Slb, the amount of increase in optical transmission loss for each wavelength A
(=S3a-8la) and B (=S3b-8lb) are calculated.

Furthermore, calculate the ratio (A/B) of this increase amount A and B,
The bending radius R can be detected based on the relationship shown in FIG. Furthermore, if the bending radius R can be determined, the bending length L can be calculated using the above equation (4).

The specific values of the transmission parameters mentioned above are the same as those of the SL type 8.
Even for M optical fibers, the refractive index distribution differs depending on how the distribution is given, so in order to calculate the bending radius R and bending length using the method described above, it is necessary to understand the transmission parameters for each end fiber 3 to be measured. I mentioned earlier that you need to do this.

However, even if the transmission parameters cannot be determined after manufacturing the optical fiber, the bending radius R and bending length can be calculated. That is, the transmission parameters of the SI type SM optical fiber can be calculated using two parameters representing the refractive index distribution, such as the core diameter and the relative refractive index difference (hereinafter referred to as structural parameters). Therefore, if the transmission parameters are not known in advance, the unknown parameters in equation (4) are the two structural parameters and the bending diameter 21.
There are a total of four bending lengths, and the optical fiber to be measured is 3.
If it is known that the optical fiber 3 is an SI type SM optical fiber, by measuring the optical transmission loss amount S in the optical fiber 3 to be measured for each wavelength using pulsed light of four different wavelengths, Parameters can be calculated: two structural parameters, bending diameter 21 bending length.

On the other hand, when there are multiple optical fibers 3 to be measured, and the relationship between the amount of increase in optical transmission loss due to bending of the multiple optical fibers and the bending shape can only be grasped statistically (for example, This method can also be applied to cases where only the average value and standard deviation of parameters that define the relationship between the amount of increase in transmission loss and the bending shape are known.

In this case, the detection result is also calculated as a statistical value.

In other words, when there are multiple optical fibers to be measured and the transmission parameters or structural parameters of these optical fibers are known statistically, for example, when the average value and standard deviation of the structural parameters are known, arbitrary bending diameter 2
The transmission loss jlS for each of the plurality of different wavelengths of light at one bending length L is also calculated as a statistical value (average value, standard deviation), and based on this, the transmission loss of the plurality of optical fibers is calculated in the same manner as described above. The average value and standard deviation of each of the bending radius R and bending length L can be calculated.

Next, a method for measuring elongation strain will be explained. The principle of measuring elongation strain has already been described in detail in the above-mentioned literature, so it will be briefly described here.

When measuring elongation strain in the measurement system shown in FIG.

Optical pulses are injected into the optical fiber 3 via the optical branching devices 4a and 4c, and optical signals from the wavelength swept light source 10 are injected into the same optical fiber 3 via the optical switch 5b and the optical branching device 4b.

As a result, when the difference between the wavelength of the light injected from the pulsed light generator 8 and the wavelength of the light injected from the wavelength sweep type light source 10 matches the brilliant wavelength shift amount caused by the stretching strain applied to the optical fiber 3. Then, the light injected from the wavelength swept light source 10 is brilliantly amplified by the light injected from the pulsed light generator 8. The amount of wavelength shift is proportional to the magnitude of distortion.

Next, the light receiving device 9 connects the light branching device 4a.

4c, wavelength swept type light source 1 via optical switches 5a and 5c
The optical power starting from 0 is monitored as a function of the wavelength of the injected light, and the results are sent to the data analysis device 11. As a result, the data analysis device 11 calculates the brilliant wavelength shift amount and further calculates the elongation strain from this value.

By summing the bending strain and elongation strain measured in this way, the rupture rate p is determined as the value of the overall strain applied to the end fiber 3 to be measured, in order to predict the breakage of the optical fiber 3.

In addition, in order to obtain this rupture rate p, a strength test is performed on an optical fiber of the same type as the optical fiber 3 to be measured, and the reference relationship between the rupture rate p and strain of the optical fiber is determined by the above-mentioned equation (2),
Alternatively, it is necessary to define the reference relationship in advance as shown in equation (3), and this reference relationship is also stored in the data analysis device 11.

Therefore, in the data analysis device 11, following the calculation of the above-mentioned comprehensive amount of strain, this calculation result is substituted into equation (2) or equation (3) to obtain the rupture rate p.

Note that, as described above, when predicting the rupture rate p at a location where it is clear that only one of the two strains, ie, bending strain and elongation strain, is applied, measurement of the other strain can be omitted.

Next, a method of predicting the future breakage rate from the past breakage rate of optical fibers of the same type manufactured under the same conditions and installed under the same circumstances will be described.

As mentioned above, this method is used to predict the rupture rate in locations where strain measurement cannot be performed due to the dynamic range of the measuring device. Whether or not the optical fiber 3 is broken can be easily detected by the optical pulse tester 6 or the optical pulse tester 7. Therefore, it is necessary to record the results in the database 12 together with information such as the rupture time and rupture location. Furthermore, information on which optical fibers were manufactured under the same conditions and installed under the same circumstances is also recorded in advance in the database 12.

Based on the past breakage rates of optical fibers manufactured under the same conditions and installed under the same conditions as the optical fiber to be predicted, stored in this database 12, the data analysis device 11 calculates the Strain S is calculated from equation (2) or equation (3), and further, based on that distortion S, (2
) or (3), the rupture rate at future time t is calculated.

At this time, as mentioned above, if there have been multiple ruptures in the past, the rupture time t+h・1~i) and the rupture probability p+(
The strain S is obtained from the i-set data of +.1 to 1) by the method of least squares.

Next, the strain was also measured and the rupture rate p
A method for predicting the future rupture rate p with high precision by combining the two measurement results will be described.

In this method, the optical pulse tester 6 is
and 7, the strain value calculated by the data analysis device 11 based on the data from the light receiving device 9 and the wavelength swept light source 10, and the strain value recorded in the database 12, which is manufactured under the same conditions as the optical fiber to be predicted. , and the strain value calculated by the data analysis device 11 based on the past breakage rate of optical fibers installed under the same conditions, the data analysis device 11 again uses the least squares method to calculate the A strain value with a small error is calculated, and this calculation result is again substituted into the above equation (2) or (3), and the rupture rate p is calculated by the data analysis device 11.
Calculated by

Next, a method for calculating strain with less error using the least squares method will be described in detail, taking as an example the case where the relationship between the rupture rate p and the strain S follows equation (2).

Here, let so be the magnitude of the strain determined by measurement, and let δS be the measurement accuracy. In addition, the rupture time in the past recorded rupture occurrence is 1+(+・1~i), the rupture rate at time t1 is pl, the expected value of the error of (In(pI) is δpI, the minimum Letting ss be a distortion with a small error calculated by the method of squares, ss is given as S such that W in equation (5) is minimized.

W=(s-so)2/δs2+Σ(In(pr
)-(m/(n-2)itj bow(m・n/(n-2))In(s)-k)2/6p+
2-(5) Also, if the number of optical fibers manufactured under the same conditions and installed under the same conditions as the optical fiber to be predicted is N, then the rupture rate at time t, p+(
i=1~1) is the equation (8), and the expected value of sampling error δp
1 is given by equation (7).

p+=l/N...(6
) δp + = (1/In(1-pl))2・p・(
N-i+1)/N2(1=11)...(7
) (Effects of the Invention) As explained above, according to claim (1), the breakage rate of an optical fiber can be predicted in advance. Therefore, based on this result, the use of optical fibers predicted to have a high breakage rate can be discontinued, or optical fibers in locations predicted to have a high breakage rate can be replaced or repaired (e.g., by removing strain). As a result, it is possible to prevent the transmission line from being interrupted due to static fatigue breakage of the optical fiber.

Optical fibers have a large communication capacity, so the prevention of communication interruptions achieved here is of great significance from the perspective of ensuring the smooth functioning of society as a whole. In addition, this method can be achieved by remotely measuring the characteristics of optical fibers installed over a wide range outdoors, and can be said to be an extremely simple method.

According to claim (2) or (3), in addition to the effect of claim (1), it is possible to predict the rupture rate in locations where strain measurement cannot be performed due to the dynamic range of the measuring device. There are advantages.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an example of a measurement system used in the present invention;
FIG. 2 is a diagram showing the relationship between the ratio of optical transmission loss amount and the bending diameter. In the figure, 1... Main signal transmitting device, 2... Main signal receiving device, 3... Optical fiber to be measured, 4a, 4b. 4c... Optical branching device, 5a, 5b, 5c... Optical switch, 6.7... Optical pulse tester, 8... Pulse light generator, 9... Light receiving device, 10... Wavelength sweep type light source, 11... data analysis device, 12... database. Patent Applicant Nippon Telegraph and Telephone Corporation Agent Patent Attorney Yoshi Yoshi 1) Figure 2 shows the relationship between optical transmission loss ratio and bending diameter

Claims (3)

[Claims] (1) Perform a strength test on an optical fiber of the same type as the optical fiber to be measured to determine the standard relationship between the breakage rate and strain of the optical fiber, and then propagate light of a predetermined wavelength through the optical fiber to be measured. , detecting this propagating light to measure the amount of strain in the optical fiber to be measured, and calculating the rupture rate of the optical fiber to be measured from the measured amount of strain and the reference relationship. Prediction method. (2) Perform a strength test on an optical fiber of the same type as the optical fiber to be measured, define a reference relationship between the breakage rate and strain of the optical fiber, and select the optical fiber of the same type as the optical fiber to be measured. Install the same type of optical fiber under the same conditions as the optical fiber, measure the breakage rate of the same type of optical fiber from the time of installation to the present time, calculate the amount of strain of the same type of optical fiber from the measured breakage rate and the reference relationship, and A method for predicting breakage of an optical fiber, comprising calculating a future breakage rate of the optical fiber to be measured from the calculated strain amount and the reference relationship. (3) Perform a strength test on an optical fiber of the same type as the optical fiber to be measured, define a reference relationship between the breakage rate and strain of the optical fiber, and propagate light of a predetermined wavelength through the optical fiber to be measured. In addition to detecting this propagating light and measuring the amount of strain in the optical fiber to be measured, an optical fiber of the same type as the optical fiber to be measured is installed under the same conditions as the optical fiber to be measured, and the results from the time of installation to the present are measured. Measure the breakage rate of the same kind of optical fiber, calculate the strain amount of the same kind of optical fiber from the measured breakage rate and the reference relationship, and calculate the estimated strain amount from the calculated strain amount and the measured strain amount. and calculating a future breakage rate of the optical fiber to be measured from this estimated strain amount and the reference relationship.