JP2003279443A - Optical fiber evaluation method and evaluation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber evaluation method and an evaluation device capable of evaluating surely abnormality of an optical fiber from an OTDR waveform. <P>SOLUTION: This optical fiber evaluation device 1 is equipped with a waveform measuring part 2 for measuring the OTDR waveform relative to the optical fiber F which is an evaluation object, and a waveform evaluation part 3 for evaluating the abnormality of the optical fiber by using the measured waveform. The waveform evaluation part 3 is constituted from a calculation part 4 and a determination part 5. In the calculation part 4, the inclination and the inclination variation at each point of time of the waveform are calculated by an inclination calculation part 41 and an inclination variation calculation part 42. In the determination part 5, it is judged whether each of the inclination and the inclination variation is within a set allowable inclination range and a set allowable change range or not by an inclination determination part 51 and an inclination variation determination part 52, to thereby determine the abnormality of the optical fiber. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber evaluation method and an evaluation device for evaluating an optical fiber using an OTDR waveform measured by an OTDR device.

[0002]

2. Description of the Related Art An OTDR waveform (Optical Time-D
omainReflectometer, an optical time domain reflectometer) has been used to evaluate optical fiber anomalies. Such an optical fiber evaluation method is disclosed, for example, in JP-A-10-332530 and JP-A-9-2692.
No. 79 publication.

In the optical fiber evaluation method based on the OTDR waveform, the optical fiber to be evaluated is connected to the OTDR device and pulsed light is incident on the optical fiber. And
O due to backscattering generated at each position of the optical fiber
The optical power returned to the TDR device is detected, and the optical fiber is evaluated from the waveform (OTDR waveform) for that time. O
The return light to the TDR device corresponds to the optical loss at each position of the optical fiber, and therefore the abnormality of the optical fiber can be evaluated from the abnormal point of its waveform.

[0004]

In the above-mentioned optical fiber evaluation method, it is important to surely determine the abnormality in the optical fiber from the measured OTDR waveform. On the other hand, Japanese Unexamined Patent Publication No. 10-332530 discloses that the average loss value in the measured waveform or a standard value in place of it is used to print the difference from the standard value of the loss value at each time point. Has been done. Where this method
Based on the difference data from the printed standard value,
The abnormality of the optical fiber is judged by the visual inspection of the evaluator. For this reason, the criteria for determining the abnormality is not clear, and the abnormality of the optical fiber cannot be reliably evaluated.

Further, in Japanese Unexamined Patent Publication No. 9-269279, an approximate straight line is obtained from the OTDR waveform by the method of least squares, and a point at which the smoothed waveform and the approximate straight line intersect with each other, the waveform at that point It is described that an abnormality in the optical fiber is determined from the inclination of the optical fiber and the length in which the inclination is in the same direction. However, this method has a problem that the abnormality of the optical fiber cannot be determined unless the waveform and the approximate straight line intersect.

The present invention has been made to solve the above problems, and an optical fiber evaluation method capable of reliably evaluating an abnormality of an optical fiber from an OTDR waveform,
And an evaluation device.

[0007]

In order to achieve such an object, an optical fiber evaluation method according to the present invention detects a return light power from an optical fiber by injecting pulsed light into the optical fiber to be evaluated. An evaluation method for evaluating an optical fiber by measuring a waveform of return light power with respect to time, including (1) an inclination calculation step of calculating an inclination at each time point of the waveform, and (2) a calculated inclination An inclination determination step of determining an abnormality of the optical fiber depending on whether or not the value is within a predetermined range.

Further, the optical fiber evaluation apparatus according to the present invention detects the optical power of return light from the optical fiber by injecting pulsed light into the optical fiber to be evaluated, and measures the waveform of the returned optical power with respect to time. An evaluation device for evaluating a fiber, comprising: (1) an inclination calculating means for calculating an inclination of a waveform at each time point; and (2) an optical fiber depending on whether the calculated inclination value is within a predetermined range. Inclination determining means for determining the abnormality is also provided.

In the above-described optical fiber evaluation method and evaluation apparatus, the slope which is the first derivative of the OTDR waveform corresponding to the local loss value at each position of the optical fiber is calculated, and the value of the slope is predetermined. The abnormality of the optical fiber is evaluated depending on whether or not it is within the range (for example, within the set allowable inclination range). Thus, instead of using the correlation between the waveform and the approximate straight line, by directly using the value of the slope of the waveform to evaluate, the presence or absence of abnormality and the position of the abnormal point are accurately determined, It is possible to reliably evaluate the abnormality of the optical fiber.

Alternatively, in the optical fiber evaluation method according to the present invention, pulsed light is incident on the optical fiber to be evaluated, the return light power from the optical fiber is detected, and the optical waveform is measured by measuring the waveform of the return light power with respect to time. An evaluation method for evaluating a fiber, comprising: (3) an inclination change amount calculation step of calculating an inclination change amount between respective time points of a waveform;
(4) An inclination change amount determining step of determining an abnormality of the optical fiber depending on whether or not the calculated inclination change amount is within a predetermined range.

Further, the optical fiber evaluation apparatus according to the present invention detects a return light power from the optical fiber by injecting pulsed light into the optical fiber to be evaluated, and measures the waveform of the return light power with respect to time. An evaluation device for evaluating a fiber, comprising: (3) a slope change amount calculating means for calculating a change amount of a slope between waveform points, and (4) the calculated slope change amount is within a predetermined range. An inclination change amount determining means for determining abnormality of the optical fiber is provided.

In the above-described optical fiber evaluation method and evaluation apparatus, the amount of change in the slope, which is the second derivative of the OTDR waveform corresponding to the local change in the loss value at each position of the optical fiber, is calculated, The abnormality of the optical fiber is evaluated depending on whether the inclination change amount is within a predetermined range (for example, within a set allowable change range). In this way, by performing evaluation using the value of the amount of change in the slope of the waveform, similar to the evaluation using the value of the slope, it is possible to accurately determine the presence or absence of an abnormality, the position of the abnormal point, etc. It is possible to reliably evaluate the abnormality. Further, by using the inclination value of the OTDR waveform and the inclination change amount together, it becomes possible to more reliably evaluate the abnormality of the optical fiber.

Here, regarding the calculation of the slope of the OTDR waveform, in the slope calculation step (slope calculation means), the waveform is divided into a plurality of sections with respect to time, and the slopes calculated within the section are averaged for each section. It is preferable to calculate the inclination by converting the value into a gradient. As a result, the influence of the statistical fluctuation of the waveform data can be removed, and the optical fiber can be evaluated well.

Further, in the calculation of the inclination change amount of the OTDR waveform, the waveform is divided into a plurality of sections with respect to time in the inclination change amount calculation step (inclination change amount calculation means) as in the calculation of the inclination. It is preferable to calculate the tilt change amount by averaging the tilt change amounts calculated within the section for each section. As a result, the influence of the statistical fluctuation of the waveform data can be removed, and the optical fiber can be evaluated well.

An optical fiber evaluation method (evaluation apparatus)
For an abnormal point for which an abnormality of the optical fiber is determined, a first approximate straight line in a predetermined section before the abnormal point and a second approximate straight line in a predetermined section after the abnormal point are obtained, and The difference between the first approximate straight line and the second approximate straight line is calculated, and depending on whether the calculated difference value is within a predetermined range,
An abnormality determination step (abnormality determination means) for determining abnormality of the optical fiber is provided.

As described above, in addition to the evaluation of the abnormality of the optical fiber using the inclination of the waveform and the like, the difference between the approximate straight lines before and after the abnormal point where the abnormality of the optical fiber is determined is obtained, and the abnormal point is detected. You can evaluate the size of the anomaly in. Further, by using the evaluation of the magnitude of the abnormality, it becomes possible to prevent a minute variation due to noise or the like from being erroneously determined as an abnormal point.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of an optical fiber evaluation method and an evaluation apparatus according to the present invention will be described in detail below with reference to the drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.
Further, the dimensional ratios in the drawings do not always match those described.

Here, the slope which is the first derivative of the OTDR waveform corresponds to the local loss value at each position of the optical fiber. Therefore, in the following, regarding the sign of the slope of the waveform, the direction in which the slope increases and the loss value in the optical fiber increases increases in the positive direction, and the direction in which the slope decreases and the loss value decreases in the optical fiber decreases. It will be described as a negative direction.

FIG. 1 is a block diagram showing the configuration of an embodiment of an optical fiber evaluation apparatus according to the present invention. The optical fiber evaluation apparatus 1 includes a waveform measurement unit 2 that measures an OTDR waveform and a waveform evaluation unit 3 that evaluates the measured waveform. Further, the waveform evaluation section 3 is composed of a calculation section 4 for calculating a data value required for the evaluation of the optical fiber, and a judgment section 5 for judging an abnormality of the optical fiber from the calculated data value. Hereinafter, the configuration of the optical fiber evaluation apparatus 1 will be described together with its operation and the optical fiber evaluation method.

First, the waveform measuring section 2 corresponding to the OTDR measuring device will be described. The waveform measuring unit 2 includes a pulsed light transmission unit 21, an optical coupler 22, and a return light reception unit 23. The pulsed light transmitter 21 is composed of, for example, a semiconductor laser, and generates and outputs pulsed light having a predetermined wavelength and a predetermined time width used for measuring the OTDR waveform. The pulsed light transmitter 21 is optically connected to an optical fiber F, which is an evaluation target of the optical fiber evaluation apparatus 1, via an optical coupler 22.

In addition to the pulsed light transmission unit 21, a return light reception unit 23 is optically connected to the optical fiber F via an optical coupler 22. The return light receiving unit 23 is formed of, for example, a semiconductor light receiving element, detects light of a predetermined wavelength input from the optical fiber F, and outputs a detection signal.

In such a configuration, when the pulsed light for evaluating the optical fiber is transmitted from the pulsed light transmitter 21 to the optical fiber F through the optical coupler 22, the optical fiber F
At each position of 1, the return light to the waveform measuring unit 2 is generated by the backscattering. This return light is received and detected by the return light receiver 23 via the optical coupler 22. Thereby, the return light and its power are detected at each time point after the pulsed light is transmitted.

The detection signal of the return light power output from the return light receiving section 23 is input to the signal processing section 24 composed of circuit elements necessary for signal processing such as an A / D converter. The signal processing unit 24 performs signal processing of the detection signal from the return light receiving unit 23 in synchronization with the pulsed light transmission time of the pulsed light transmission unit 21.

More specifically, the signal processing unit 24 including an A / D converter and the like has a large number of units at a constant cycle from the sampling start time, which is a fixed time after the pulsed light transmission unit 21 transmits the pulsed light. The measured return light power is sampled at each sampling time. This sampling data becomes the original data of the OTDR waveform which is the waveform of the return light power with respect to time.

Here, the time difference between the pulsed light transmission time at the pulsed light transmission unit 21 and the sampling time, which is the time at which the returned light reception unit 23 and the signal processing unit 24 receive the returned light, is determined by the optical fiber F. Is the delay time until the optical component of the transmitted pulsed light is backscattered and returns. That is, this time difference corresponds to the position in the optical fiber F where the measured return light is backscattered. Therefore, the OTDR waveform of this return light power with respect to time is measured,
By evaluating the presence / absence of an abnormality in the waveform and the delay time at which the abnormality occurs, it is possible to evaluate the presence / absence of an abnormality in the evaluation target optical fiber F and the position of the abnormality point.

The operation of each unit in the waveform measuring unit 2 is controlled by the measurement control unit 20. Measurement control unit 20
Indicates to the pulsed light transmitter 21 the transmission time of the pulsed light. Further, the measurement control unit 20 refers to the transmission time of the pulsed light, and instructs the signal processing unit 24 about the sampling time of the detection signal from the return light reception unit 23, which is the reception time of the return light. Further, each data such as return light sampling data sampled by the signal processing unit 24 is collected by the measurement control unit 20.

Next, the waveform evaluation section 3 corresponding to the OTDR evaluation device will be described. The waveform evaluation unit 3 includes a calculation unit 4
And the determination unit 5.

The calculator 4 has a waveform generator 40, a slope calculator 41, and a slope change amount calculator 42. The waveform generation unit 40 inputs necessary data such as return light sampling data collected by the measurement control unit 20 of the waveform measurement unit 2, and generates an OTDR waveform for the time of the return light power based on the data. To do. The delay time in the waveform with respect to this time is, as described above, the optical fiber F
It corresponds to the position in.

The slope calculator 41 calculates the slope which is the first-order differential at each time point of the OTDR waveform generated by the waveform generator 40 (slope calculation step). In addition, the slope change amount calculation unit 42 calculates the slope change amount (the slope change amount between each time point, the first-order differential of the slope) that is the second-order differential at each time point for the OTDR waveform (slope change). Amount calculation step). The value of the slope and the amount of change in the slope of these waveforms at each time point are used by the determination unit 5 to evaluate the abnormality of the optical fiber.

The judging section 5 has a tilt judging section 51, a tilt change amount judging section 52, and an abnormality judging section 50.

In the inclination determining section 51, an allowable range (for example, an allowable inclination range as an allowable numerical value range) is set for the inclination of the OTDR waveform calculated by the inclination calculating section 41. The inclination determining unit 51 determines whether the calculated inclination value of the waveform is within a predetermined range, and based on the result, determines whether the optical fiber F is abnormal (inclination determining step). In addition, the inclination change amount determination unit 52
In the above, an allowable range (for example, an allowable change range) is set for the inclination change amount of the OTDR waveform calculated by the inclination change amount calculation unit 42. Tilt change amount determination unit 52
Determines whether or not the calculated inclination change amount of the waveform is within a predetermined range, and determines whether or not the optical fiber F is abnormal based on the result (inclination change amount determination step).

Further, the abnormality determining section 50 includes an inclination determining section 51.
The presence / absence of an abnormality in the evaluation target optical fiber F and the position of the abnormal point are determined based on the determination result of the inclination change amount determination unit 52 and the like (abnormality determination step).

The effects of the optical fiber evaluation apparatus and the evaluation method according to the present embodiment will be described.

In the optical fiber evaluation apparatus and the evaluation method using the same shown in FIG. 1, the optical fiber F to be evaluated with respect to the OTDR waveform measured by the waveform measuring section 2 is measured.
The slope (first derivative) of the waveform corresponding to the local loss value at each position is calculated, and the abnormality of the optical fiber F is evaluated depending on whether the slope value is within a predetermined range. . As described above, by performing evaluation using the value of the slope of the OTDR waveform, it is possible to accurately determine the presence or absence of an abnormality, the position of an abnormal point, and the like.

For example, using an approximate straight line for a waveform,
When using a method to evaluate the abnormality of the optical fiber from the point where the waveform and the approximate straight line intersect, as long as the correlation with the approximate straight line is normal, the abnormality can be judged even if the waveform itself is abnormal. Can not. On the other hand, according to the evaluation method that directly uses the value of the waveform inclination itself, it is possible to reliably evaluate the abnormality of the optical fiber.

Further, in the present embodiment, the slope change amount (second derivative) of the waveform corresponding to the local change of the loss value is calculated for the OTDR waveform, and the slope change amount is within a predetermined range. The abnormality of the optical fiber F is evaluated depending on whether or not it is inside. As described above, by performing the evaluation using the inclination change amount of the OTDR waveform, it is possible to accurately determine the presence or absence of an abnormality, the position of the abnormal point, and the like, similarly to the evaluation using the inclination value. Further, by using the inclination value of the OTDR waveform and the inclination change amount together, it becomes possible to more reliably evaluate the abnormality of the optical fiber. It should be noted that a specific method for evaluating the abnormality of the optical fiber using the tilt and the tilt change amount will be described later.

Here, the OTDR in the inclination calculation unit 41
Regarding the calculation of the slope of the waveform, it is preferable to divide the waveform into a plurality of sections with respect to time and average the slopes calculated in the section to calculate the slope. That is, the measured waveform data is a discontinuous value due to data fluctuations, noise, etc., and it is difficult to simply formulate the waveform to obtain the derivative. Therefore, the slope of the waveform is calculated, for example, by taking the difference between two adjacent data points of the waveform.

Specifically, since the return light sampling data obtained by the waveform measuring unit 2 has a large statistical fluctuation, etc., the waveform generating unit 40 normally performs a smoothing process using a moving average or the like. , Waveform data is generated. Then, the slope of the waveform is calculated from the difference between two adjacent data points of the waveform data. However,
Even when the waveform data after such moving average processing is used, the inclination may not be calculated sufficiently accurately due to the influence of the remaining data fluctuation.

In such a case, as described above, a section including a plurality of data points is set for the waveform data with a predetermined time width, and the slope is averaged in this section to obtain a section. Slope of (eg slope at the first point of the interval)
By calculating, it is possible to remove the influence of the statistical fluctuation of the waveform data and to evaluate the optical fiber satisfactorily. Similarly, in the calculation of the inclination change amount of the OTDR waveform in the inclination change amount calculation unit 42, the waveform can be divided into a plurality of sections with respect to time, and the inclination change amount can be calculated by averaging each section. preferable.

For averaging the slope and the amount of change in the slope within a section, various averaging methods may be used. Alternatively, when the fluctuation of the waveform data is sufficiently small, the averaging may not be performed.

Regarding the abnormality determination of the optical fiber F in the abnormality determination section 50, the abnormality determination may be performed immediately from the determination result in the inclination determination section 51 or the inclination change amount determination section 52, but still another method. It is also possible to repeatedly determine the abnormality using. For example, in the abnormality determination unit 50, in addition to the presence or absence of abnormality, the position of the abnormality point, and the like, regarding the abnormal point of the optical fiber that is determined to be abnormal by the determination result of the inclination determination unit 51 or the inclination change amount determination unit 52, The magnitude of the abnormality at the abnormal point may be evaluated.

Further, utilizing the evaluation of the magnitude of this abnormality,
By determining the abnormality of the optical fiber based on whether or not the magnitude of the abnormality is within a predetermined range, it is possible to prevent a minute fluctuation due to noise or the like from being erroneously determined as an abnormal point. As a concrete evaluation method of the magnitude of such an abnormality, for example, a first approximation straight line in a predetermined section before the abnormal point of the optical fiber and a second approximation line in a predetermined section after the abnormal point A method of evaluating the magnitude of the abnormality can be used by obtaining the straight line and calculating the difference between the two approximate straight lines at the abnormal point. Also, for the difference of the approximate straight line at this abnormal point, the allowable range (for example,
By setting the allowable difference range) as the allowable numerical range, it becomes possible to more reliably determine the abnormality of the optical fiber together with the determination based on the slope of the waveform or the slope change amount.

A method for evaluating the abnormality of the optical fiber using the inclination of the OTDR waveform will be described with a specific example. Here, the horizontal axis in each of the graphs shown below indicates the fiber length (position in the optical fiber F to be evaluated). This fiber length corresponds to the delay time from the transmission of the pulsed light by the pulsed light transmitter 21 to the reception of the returned light by the return light receiver 23.

FIG. 2 shows (a) OTDR waveform, and (b).
It is a graph which shows an example of the time change of the inclination which is the first derivative of a waveform. The inclination graph of FIG. 2B shows the allowable inclination range set for the inclination value.

In this example, as shown in FIG. 2 (a), an example of a step-like time change in which the waveform sharply decreases in the vicinity of the abnormal center point C is shown. At this time, the slope of the waveform fluctuates once in the positive direction (the direction in which the slope increases) as shown in FIG. Therefore, in the vicinity of this abnormal point, it is possible to determine the step-like abnormality in the optical fiber by detecting the variation in which the value of the inclination becomes larger than the upper limit of the allowable inclination range. Further, the position of the abnormal center point C in the optical fiber is obtained from the point A at which the inclination becomes maximum.

FIG. 3 shows (a) OTDR waveform, and (b).
It is a graph which shows the other example of the time change of the inclination of a waveform.

In this example, as shown in FIG. 3 (a), an example of a ridge-like temporal change in which the waveform sharply increases in the vicinity of the abnormal center point C is shown. At this time, the slope of the waveform fluctuates once in the negative direction (direction in which the slope decreases) as shown in FIG. Therefore, in the vicinity of this abnormal point, it is possible to determine a bump-like abnormality in the optical fiber by detecting a variation in which the value of the inclination becomes smaller than the lower limit of the allowable inclination range. Further, the position of the abnormal center point C in the optical fiber can be obtained from the point A where the inclination becomes the minimum.

FIG. 4 shows (a) OTDR waveform and (b)
It is a graph which shows the other example of the time change of the inclination of a waveform.

In this example, as shown in FIG. 4 (a), an example of a temporal change in a protrusion shape in which the waveform temporarily increases in the vicinity of the abnormal center point C is shown. At this time, the slope of the waveform fluctuates twice in the negative direction and the positive direction as shown in FIG. Therefore, in the vicinity of this abnormal point, it is possible to determine a protrusion-like abnormality in the optical fiber by detecting a variation in which the inclination value becomes smaller than the lower limit of the allowable inclination range and then becomes larger than the upper limit. . Further, the position of the abnormal center point C in the optical fiber is obtained by the point A where the inclination is between the minimum and maximum and the difference from the average value of the inclination is 0.

FIG. 5 shows (a) OTDR waveform, and (b)
It is a graph which shows the other example of the time change of the inclination of a waveform.

In this example, as shown in FIG. 5 (a), an example of an inverse projection-like temporal change in which the waveform is temporarily reduced in the vicinity of the abnormal center point C is shown. At this time, the slope of the waveform fluctuates twice in the positive direction and the negative direction as shown in FIG. Therefore, in the vicinity of this abnormal point, it is possible to determine an inverted protrusion-like abnormality in the optical fiber by detecting a variation in which the value of the inclination becomes larger than the upper limit of the allowable inclination range and then becomes smaller than the lower limit. it can. Further, the position of the abnormal center point C in the optical fiber is obtained by the point A where the inclination is between the maximum and the minimum and the difference from the average value of the inclination is 0.

As described above, according to the method of setting the allowable inclination range for the inclination of the OTDR waveform and determining the abnormality when the value of the inclination is out of the allowable inclination range, the presence or absence of abnormality in the optical fiber is detected. The position of the abnormal point or the abnormal center point can be reliably evaluated. Further, it is also possible to determine the type of abnormality such as a step, a ridge, a protrusion, and a reverse protrusion from the time change of the inclination.

There are several possible setting methods for setting the allowable tilt range for the waveform tilt. For example, there is a method of setting an absolute numerical range for the inclination and setting the numerical range as an allowable inclination range. With such a setting method, there is an advantage that it is possible to prevent the variation of the inclination in the vicinity of the abnormal point from affecting the abnormality determination.

Alternatively, there is a method in which an approximate straight line is obtained with respect to the time change of the inclination, the average value of the inclination is calculated, and the allowable inclination range is set by the numerical range based on the average value of the inclination. With such a setting method, it is easy to set the reference value for the abnormality determination, and it is easy to determine the abnormality in the optical fiber by observing the change from the average value.

Alternatively, there is a method of setting the allowable tilt range by a numerical range based on the tilt at the previous data point. Such a setting method has an advantage that it is possible to prevent a local abnormality from being easily determined because it is possible to prevent the variation in the inclination in the vicinity of the abnormal point from affecting the abnormality determination.

Regarding the setting of the allowable tilt range with respect to the tilt of the waveform, one of the above-mentioned setting methods or a combination of these setting methods is appropriately selected depending on the performance of the optical fiber to be evaluated, the waveform measuring device, and the like. It is preferable to use. Also, setting methods other than the above may be used.

Next, a method of evaluating an abnormality of the optical fiber using the inclination change amount of the OTDR waveform will be described with reference to a concrete example.

By using the slope of the OTDR waveform,
It is possible to evaluate the abnormality of the optical fiber as described above. Here, the slope, which is the first derivative of the waveform, is easily affected by the shape of the waveform in the vicinity of the abnormal point. Therefore, when it is necessary to determine the abnormal range of the abnormality in the optical fiber, the starting point and the ending point of the abnormality may not be calculated with sufficient accuracy. On the other hand, using the slope change amount that is the second derivative of the waveform (first derivative of the slope) has an advantage that the variation point of the waveform caused by the abnormality can be easily understood.

FIG. 6 shows (a) OTDR waveform, and (b).
It is a graph which shows an example of the time change of the amount of change of inclination which is the second derivative of a waveform. Further, the graph of the amount of change in inclination in FIG. 6B shows the allowable change range set for the amount of change in inclination.

In this example, as shown in FIG. 6 (a), an example of a stepwise time change in which the waveform suddenly decreases in the vicinity of the abnormal center point C is shown (see FIG. 2). At this time, the amount of change in the slope of the waveform fluctuates twice in the positive direction and the negative direction as shown in FIG. Therefore, in the vicinity of this abnormal point, it is possible to determine a step-like abnormality in the optical fiber by detecting a change in which the amount of change in inclination becomes larger than the upper limit of the allowable change range and then becomes smaller than the lower limit. . Further, the position of the abnormal center point C in the optical fiber can be obtained from the point B at which the amount of change in inclination is between the maximum and the minimum and becomes zero.

FIG. 7 shows (a) OTDR waveform, and (b)
8 is a graph showing another example of the change over time in the amount of change in the slope of the waveform.

In this example, as shown in FIG. 7A, an example of a ridge-like temporal change in which the waveform suddenly increases in the vicinity of the abnormal center point C is shown (see FIG. 3). At this time, the amount of change in the inclination of the waveform fluctuates twice in the negative direction and the positive direction as shown in FIG. 7B. Therefore, in the vicinity of this abnormal point, it is possible to determine a bump-like abnormality in the optical fiber by detecting a change in which the amount of change in inclination becomes smaller than the lower limit of the allowable change range and then becomes larger than the upper limit. . Further, the position of the abnormal center point C in the optical fiber can be obtained from the point B where the amount of change in inclination is between the minimum and the maximum and becomes zero.

FIG. 8 shows (a) OTDR waveform and (b)
8 is a graph showing another example of the change over time in the amount of change in the slope of the waveform.

In this example, as shown in FIG. 8A, there is shown an example of a temporal change in a protrusion shape in which the waveform temporarily increases in the vicinity of the abnormal center point C (see FIG. 4). At this time, the amount of change in the slope of the waveform fluctuates three times in the negative direction, the positive direction, and the negative direction as shown in FIG. Therefore, in the vicinity of this abnormal point, the change in the inclination change amount becomes smaller than the lower limit of the allowable change range, then becomes larger than the upper limit, and then becomes smaller than the lower limit. Abnormalities can be determined. Further, the position of the abnormal center point C in the optical fiber is obtained from the point B at which the amount of change in the inclination becomes maximum.

FIG. 9 shows (a) OTDR waveform, and (b).
8 is a graph showing another example of the change over time in the amount of change in the slope of the waveform.

In this example, as shown in FIG. 9A, there is shown an example of an inverse projection-like temporal change in which the waveform is temporarily reduced in the vicinity of the abnormal center point C (see FIG. 5).
At this time, the amount of change in the inclination of the waveform fluctuates three times in the positive direction, the negative direction, and the positive direction as shown in FIG. 9B.
Therefore, in the vicinity of this abnormal point, the amount of change in inclination becomes larger than the upper limit of the allowable change range, then becomes smaller than the lower limit, and then becomes larger than the upper limit. It is possible to determine a protrusion-like abnormality. Also, the point B at which the amount of change in the inclination becomes a minimum causes the abnormal center point C in the optical fiber
The position of is required.

As described above, according to the method of setting the allowable change range for the slope change amount of the OTDR waveform and determining the abnormality when the slope change amount is out of the allowable change range, the slope of the waveform is determined. Similar to the method used, it is possible to reliably evaluate the presence or absence of abnormality in the optical fiber, the position of the abnormal point or the abnormal center point, and the like. In addition, from the time change of the slope change amount,
It is also possible to determine the types of abnormalities such as steps, bumps, protrusions, and reverse protrusions.

Further, in the method using the amount of change in slope of the waveform, the amount of change in slope, which is the second derivative, is larger than that of the slope, which is the first derivative, and the values at the start and end points of the abnormal range are large. The fluctuation is sharp. Therefore, the starting point and the ending point of the abnormal range can be obtained more accurately. However, since the amount of inclination change is easily affected by a minute waveform due to noise or the like, when the influence of noise or the like is a problem in the abnormality determination, the determination method using the inclination and the determination method using the inclination change amount are used. It is preferable to use them together. Alternatively, if one of the determination methods using the inclination or the inclination change amount can make a sufficiently accurate abnormality determination, the determination may be performed based on only one of the inclination and the inclination change amount.

Here, in the above-described optical fiber abnormality determination method using the inclination of the OTDR waveform and the inclination change amount,
There is a case in which the minute fluctuations are erroneously determined to be abnormal due to the detection of the tilt or the rapid fluctuation of the tilt change amount due to the minute fluctuations due to noise or the like. On the other hand, in addition to the evaluation using the slope of the waveform and the like, by obtaining the difference between the approximate straight lines before and after the abnormal point, it is possible to evaluate the magnitude of the abnormality at the abnormal point. Further, by using the evaluation of the magnitude of the abnormality, it becomes possible to prevent a minute variation from being mistakenly determined to be an abnormality.

FIG. 10 is a graph showing an example of changes over time in (a) OTDR waveform, (b) waveform slope, and (c) waveform slope change amount.

In this example, as shown in FIG. 10 (a), an example of a stepwise time change in which the waveform suddenly decreases in the vicinity of the abnormal center point is shown (see FIGS. 2 and 6).
When an abnormality due to such a time change is determined using the slope that is the first derivative of the waveform, first, the center point of the determined abnormality range is set to the abnormal point P for evaluating the magnitude of the abnormality.
And

For this abnormal point P, the first approximate straight line L ₁ is obtained from the waveform within a predetermined section (for example, a section with a constant inclination) before the start point of the determined abnormal range. Also,
The second approximate straight line L ₂ is obtained from the waveform in the predetermined section after the end point of the abnormal range. Then, as shown in FIG. 10A, a difference Δs between the value of the first approximate straight line L _{1 and} the value of the second approximate straight line L ₂ at the abnormal point P is obtained.

From the difference Δs, the size of the step-like abnormality at the abnormal point P can be evaluated. Further, it is possible to determine whether or not the abnormality of the optical fiber is a minute step-like variation depending on whether or not the value of the difference Δs is within the set allowable difference range. Even when the abnormality is determined by using the amount of change in inclination which is the second derivative of the waveform, the magnitude of the abnormality can be evaluated by the same method.

FIG. 11 is a graph showing another example of temporal changes in (a) OTDR waveform, (b) waveform slope, and (c) waveform slope change amount.

In this example, as shown in FIG. 11 (a), an example of a ridge-like temporal change in which the waveform sharply increases in the vicinity of the abnormal center point (see FIGS. 3 and 7).
When an abnormality due to such a time change is determined by using the slope of the waveform, first, the center point of the determined abnormality range is
The abnormal point P is used to evaluate the size of the abnormality.

With respect to this abnormal point P, a first approximate straight line L ₁ is obtained from the waveform in a predetermined section before the start point of the determined abnormal range. Further, the second approximate straight line L ₂ is obtained from the waveform in the predetermined section after the end point of the abnormal range. Then, as shown in FIG. 11A, a difference Δs between the value of the first approximate straight line L _{1 and} the value of the second approximate straight line L ₂ at the abnormal point P is obtained.

From the difference Δs, it is possible to evaluate the magnitude of the bump-like abnormality at the abnormal point P. Further, it is possible to determine whether or not the abnormality of the optical fiber is a minute ridge-like variation depending on whether or not the value of the difference Δs is within the set allowable difference range. Even when the abnormality is determined using the amount of change in the slope of the waveform, the magnitude of the abnormality can be evaluated by the same method.

FIG. 12 is a graph showing another example of temporal changes in (a) OTDR waveform, (b) waveform slope, and (c) waveform slope change amount.

In this example, as shown in FIG. 12 (a), an example of a temporal change in a protrusion shape in which the waveform temporarily increases in the vicinity of the abnormal center point (see FIGS. 4 and 8). . When an abnormality due to such a temporal change is determined using the slope of the waveform, first, the start point of the determined abnormality range is set as an abnormal point P for evaluating the size of the abnormality.

With respect to this abnormal point P, the first approximate straight line L ₁ is obtained from the waveform in a predetermined section before the start point (abnormal point P) of the determined abnormal range. Further, the second approximate straight line L ₂ is obtained from the waveform within the predetermined section including the center point of the abnormal range. Then, as shown in FIG. 12A, a difference Δ between the value of the first approximate straight line L _{1 and} the value of the second approximate straight line L ₂ at the abnormal point P.
Find s.

From this difference Δs, it is possible to evaluate the size of the protrusion-like abnormality at the abnormal point P. Further, it is possible to determine whether or not the abnormality of the optical fiber is a minute protrusion-like variation depending on whether or not the value of the difference Δs is within the set allowable difference range. Even when the abnormality is determined using the amount of change in the slope of the waveform, the magnitude of the abnormality can be evaluated by the same method.

FIG. 13 is a graph showing another example of temporal changes in (a) OTDR waveform, (b) waveform slope, and (c) waveform slope change amount.

In this example, as shown in FIG. 13 (a), there is shown an example of an inverse projection-like temporal change in which the waveform temporarily decreases in the vicinity of the abnormal center point (see FIGS. 5 and 9). ). When an abnormality due to such a temporal change is determined using the slope of the waveform, first, the start point of the determined abnormality range is set as an abnormal point P for evaluating the size of the abnormality.

With respect to this abnormal point P, the first approximate straight line L ₁ is obtained from the waveform within a predetermined section before the start point (abnormal point P) of the determined abnormal range. Further, the second approximate straight line L ₂ is obtained from the waveform within the predetermined section including the center point of the abnormal range. Then, as shown in FIG. 13A, a difference Δ between the value of the first approximate straight line L _{1 and} the value of the second approximate straight line L ₂ at the abnormal point P.
Find s.

From the difference Δs, it is possible to evaluate the magnitude of the inverted protrusion-like abnormality at the abnormal point P. Further, it is possible to determine whether or not the abnormality of the optical fiber is a minute inverted protrusion-like variation depending on whether or not the value of the difference Δs is within the set allowable difference range. Even when the abnormality is determined using the amount of change in the slope of the waveform, the magnitude of the abnormality can be evaluated by the same method.

As described above, the method of evaluating the magnitude of abnormality from the difference between the two approximate straight lines before and after the abnormal point and judging the abnormality when the value of the difference is outside the allowable difference range, By using this together with the determination method based on the slope of the waveform or the amount of change in the slope, it is possible to more reliably evaluate the presence or absence of an abnormality in the optical fiber by excluding minute fluctuations due to noise or the like. Note that various methods other than the above-described examples can be used for setting an abnormal point in the determined abnormal range and determining two approximate straight lines for the abnormal point.

The optical fiber evaluation method and the evaluation apparatus according to the present invention are not limited to the above-described embodiments and examples, and various modifications can be made. For example, in the optical fiber evaluation apparatus 1 shown in FIG. 1, a waveform measurement section 2 that is an OTDR measurement apparatus is provided side by side with a waveform evaluation section 3 that evaluates an optical fiber abnormality using an OTDR waveform. However, the measuring device may be a separate device, and the optical fiber may be evaluated by reading the data of the OTDR waveform measured by the measuring device.
Further, the allowable range set for the inclination and the amount of change in inclination does not necessarily have to be constant, and may be a variable numerical range.

[0088]

As described in detail above, the optical fiber evaluation method and the evaluation apparatus according to the present invention have the following effects. That is, the slope which is the first derivative or the slope change amount which is the second derivative at each time point of the OTDR waveform is calculated, and depending on whether the calculated slope value or the slope change amount is within a predetermined range, According to the evaluation method and the evaluation device for determining the abnormality of the optical fiber, it is possible to accurately determine the presence or absence of the abnormality, the position of the abnormal point, and the like, and reliably evaluate the abnormality of the optical fiber.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of an optical fiber evaluation apparatus.

FIG. 2 is a graph showing an example of a temporal change of a slope of (a) OTDR waveform and (b) waveform.

FIG. 3 is a graph showing another example of the temporal change of the slope of the (a) OTDR waveform and (b) the waveform.

FIG. 4 is a graph showing another example of (a) OTDR waveform and (b) time-dependent change in the slope of the waveform.

5A and 5B are graphs showing another example of the temporal change of the inclination of the (A) OTDR waveform and (b) the waveform.

FIG. 6 is a graph showing an example of a change over time in the amount of inclination change of (a) OTDR waveform and (b) waveform.

FIG. 7 is a graph showing another example of the temporal change of the inclination change amount of (a) OTDR waveform and (b) waveform.

8A and 8B are graphs showing another example of the temporal change of the inclination change amount of (a) OTDR waveform and (b) waveform.

9A and 9B are graphs showing another example of the temporal change of the inclination change amount of (a) OTDR waveform and (b) waveform.

FIG. 10 is a graph showing an example of temporal changes in (a) OTDR waveform, (b) waveform slope, and (c) waveform slope change amount.

FIG. 11 is a graph showing another example of (a) OTDR waveform, (b) waveform slope, and (c) waveform slope change amount with time.

FIG. 12 is a graph showing another example of temporal changes in (a) OTDR waveform, (b) waveform slope, and (c) waveform slope change amount.

FIG. 13 is a graph showing another example of temporal changes in (a) OTDR waveform, (b) waveform slope, and (c) waveform slope change amount.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical fiber evaluation device, F ... Optical fiber, 2 ... Waveform measurement part, 20 ... Measurement control part, 21 ... Pulse light transmission part, 22
... optical coupler, 23 ... return light receiving section, 24 ... signal processing section,
3 ... Waveform evaluation unit, 4 ... Calculation unit, 40 ... Waveform generation unit, 41
... inclination calculator, 42 ... inclination change amount calculator 5, 5 ... judgment unit,
50 ... Abnormality determination unit, 51 ... Inclination determination unit, 52 ... Inclination change amount determination unit

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toshiyuki Yamamoto             Sumitomo, 1-1 1-1 Koyokita, Itami City, Hyogo Prefecture             Electric Industry Co., Ltd. Itami Works (72) Inventor Toshio Oshima             Sumitomoden 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa             Ki Industry Co., Ltd. Yokohama Works F-term (reference) 2G086 CC03

Claims (8)

[Claims] 1. An evaluation method for evaluating an optical fiber by injecting pulsed light into an optical fiber to be evaluated, detecting return optical power from the optical fiber, and measuring a waveform of the return optical power with respect to time. A slope calculating step of calculating a slope at each time point of the waveform, and a slope determining step of determining an abnormality of the optical fiber depending on whether or not the calculated slope value is within a predetermined range. An optical fiber evaluation method comprising: 2. An evaluation method for evaluating an optical fiber by injecting pulsed light into an optical fiber to be evaluated, detecting return optical power from the optical fiber, and measuring a waveform of the return optical power with respect to time. It is an inclination change amount calculation step for calculating the amount of change in inclination between the time points of the waveform, and whether or not the calculated inclination change amount is within a predetermined range indicates that the optical fiber is abnormal. An optical fiber evaluation method comprising: a tilt change amount determination step of determining. 3. An inclination change amount calculating step for calculating an amount of change in the inclination between respective time points of the waveform, and a step of calculating the inclination change amount of the optical fiber according to whether or not the calculated inclination change amount is within a predetermined range. The optical fiber evaluation method according to claim 1, further comprising an inclination change amount determination step of determining abnormality. 4. The slope calculation step, wherein the waveform is divided into a plurality of sections with respect to time, and the slopes calculated in the section are averaged for each section to calculate the slope. The optical fiber evaluation method according to claim 1. 5. In the tilt change amount calculation step,
4. The slope change amount is calculated by dividing the waveform into a plurality of sections with respect to time, and averaging the slope change amounts calculated in the section for each section. Optical fiber evaluation method. 6. An abnormal point for which an abnormality of the optical fiber is determined, a first approximate straight line in a predetermined section before the abnormal point and a second approximate straight line in a predetermined section after the abnormal point. Then, the difference between the first approximation line and the second approximation line at the abnormal point is calculated, and the abnormality of the optical fiber is determined depending on whether the calculated difference value is within a predetermined range. The optical fiber evaluation method according to claim 1 or 2, further comprising an abnormality determination step. 7. An evaluation device for evaluating the optical fiber by injecting pulsed light into an optical fiber to be evaluated, detecting return optical power from the optical fiber, and measuring a waveform of the return optical power with respect to time. A slope calculating means for calculating the slope of the waveform at each time point, and a slope determining means for determining an abnormality of the optical fiber depending on whether or not the calculated slope value is within a predetermined range. An optical fiber evaluation apparatus comprising: 8. An evaluation device for evaluating the optical fiber by injecting pulsed light into an optical fiber to be evaluated, detecting return optical power from the optical fiber, and measuring a waveform of the return optical power with respect to time. A slope change amount calculating means for calculating the change amount of the slope between the time points of the waveform, and whether or not the calculated slope change amount is within a predetermined range indicates that the optical fiber is abnormal. An optical fiber evaluation device, comprising: an inclination change amount determination means for determination.