JPS6130741A - Method and apparatus for detecting rearwardly scattered light abnormal pattern of optical fiber - Google Patents

Abstract

PURPOSE:To accurately and objectively perform the judgement of the presence or absence and kind of a flaw, by smoothing the distance curve of a BS curve, which is obtained by measuring rearwardly scattered light of an optical fiber, from the average straight line thereof and comparing the number of max. points and min. points with a reference value by using absolute values as a parameter. CONSTITUTION:The average straight line 12 of a BS curve 11 obtained by an optical pulse tester is calculated and, from the straight line 12, the BS converted curve 14 showing the distance up to each point at every definite time interval on the curve 11 is shown as continuous dots with respect to a horizontal axis 13 to be subjected to smoothing treatment. The number of max. values and min. values and the absolute values thereof are calculated with respect to the curve to which the smoothing treatment was applied to set a parameter and, with respect to a normal optical fiber, the reference value of a parameter is preliminarily calculated by smoothing treatment from a BS converted curve and the parameter is compared with the reference value thereof to judge presence or absence and kind of a flaw.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical field to which the invention pertains The present invention relates to backscattered light measurement of an optical fiber, and more specifically, to the measurement of optical fiber backscattered light based on the BS curve obtained by the backscattered light measurement of an optical fiber. The present invention relates to a method and apparatus for determining the presence or absence of a defect and its type.

(b) Prior art and its problems As a method for detecting defects in optical fibers, such as steps, undulations, double bends, etc., a backscattered light measurement method is used, as shown in FIG. 1. In Figure 1,
Pulse generator 1. The optical transmitter 2 cooperates to generate a light pulse, which is transmitted to the lens 3. The light passes through a half mirror 5 and a lens 4 and enters one end of an optical fiber 6. The light reflected inside the optical fiber 6 returns in the opposite direction as backscattered light, is reflected by the half mirror 5, passes through the lens 7, and is received by the light receiving device 8. Then, the display or recording device 9 displays the backscattered light as a received light power curve, ie, a 138 curve, with the horizontal axis representing the propagation time and the vertical axis representing the received light power. If there is a defect in the optical fiber to be measured, such as a step or a single bend, the defect is considered to be BS.
Abnormal patterns appear on the curves as shown somewhat exaggeratedly in FIGS. 2, 3, and 4, respectively. Thereby, by looking at the pattern of the BS curve, it is possible to determine the presence or absence of a defect in the optical fiber and the type of the defect. As described above, the conventional method is to judge the optical fiber by visually observing the BS curve.

However, in the conventional optical fiber backscattered light abnormal pattern detection method described above, even if there is actually a defect in the optical fiber, a clear abnormal pattern τ is not necessarily formed on the B and S curves, and Due to the influence of defects, it is often difficult to make accurate and objective judgments regarding the presence or absence and type of defects in optical fibers by visual observation of the BS curve.

Purpose of the Invention The present invention has been made in view of the above-mentioned conventional circumstances, and
It is an object of the present invention to provide a method and apparatus for detecting an abnormal pattern of backscattered light in an optical fiber, which makes it possible to accurately and objectively determine the presence or absence of a defect in an optical fiber and its type.

B) Structure of the invention The present invention is based on the BS obtained by measuring backscattered light of an optical fiber.
Converting the curve into a curve showing the distance from the average straight line to each point on the BS curve, smoothing the curve showing the distance, and calculating the maximum of the curve showing the distance after the smoothing process. The number of points and minimum points and their absolute values are used as parameters, and the presence or absence of defects in optical fibers and their types can be determined by comparing them with parameter reference values determined in advance under the same smoothing conditions. Features.

Thereby, a method and apparatus for detecting an abnormal pattern of backscattered light in an optical fiber are provided, which can accurately and objectively determine the presence or absence of a defect in an optical fiber and its type.

(E) Embodiment of the Invention An example of the BS curve showing the backscattered light characteristics obtained by the optical pulse tester is shown at 11 in FIG. The horizontal axis shows the distance or propagation time from the end of the optical fiber, and the vertical axis shows the received light power (dn).

From this BS curve 11, an average straight line 12 of the BS curve is determined. A BS conversion curve showing the distance from the average straight line 12 to each point at regular time intervals on the BS curve 11] 4 is shown as a continuous dot with respect to the horizontal axis 13 and with enlarged coordinates with respect to the vertical axis. .

When smoothing the BS curve to facilitate the determination of abnormal patterns in the BS curve as illustrated in Figs. 2 to 4, the B
Smoothing processing is performed based on the S conversion curve 14. In this example, the results of calculating the moving average of 50 points are shown in FIG. The curve in FIG. 6 has not yet been sufficiently smoothed, so despite its smoothness, it can be seen that there are many very thick and minimal points along the curve, as shown by N marks and N marks, respectively. Therefore, a moving average of 50 points was calculated based on the curve shown in FIG. 6, and the results are shown in FIG. The curve in FIG. 7 has been smoothed to a considerable extent and shows a smooth curve. Only one extremely thick point and one extremely small point exist as shown by N marks and N marks, respectively.

Normal optical fiber and various defects, here each stage,
We smoothed the BS conversion curve for an optical fiber with two undulations using the same method as described above, and examined the appearance of extremely thick and minimum points, and obtained the results shown in the table below (Table 1) ).

Table 1 Here, the maximum and minimum values of extremely thick and extremely small are in units of 1 car and 20 d.
Corresponds to Ii. The extremely thick and minimum points in Table 1 indicate that the BS curve of an optical fiber with steps, undulations, and bends generally has a pattern as shown in Figures 2 to 4. It can be seen that the characteristic turns that should appear on the 18 curve become smoother as a result of smoothing.

In other words, the macro features of the abnormal pattern of the BS curve, which are not necessarily clearly shown in the raw data of the 18 curves, are clarified by smoothing. In addition, when the optical fiber is normal, the number of extremely thick and minimum points is higher than when there is a defect.

It turns out that the absolute value of the minimum value is /''.

Based on the above results, the presence or absence of defects in an optical fiber exhibiting a BS curve using the number of extremely thick and minimum points of the smoothed BS conversion curve, the maximum value of the extremely thick, and the absolute value of the minimum value of the extremely small as parameters are determined. It turns out that it is possible to determine the type.

In other words, standard values of the above parameters are obtained in advance by smoothing processing from the BS conversion curves of optical fibers with various defects and normal optical fibers, and the BS conversion curve of the undetermined optical fiber is smoothed under the same conditions. By comparing the parameter values obtained from the above with reference values, it is possible to determine the presence or absence of a defect in the optical fiber and its type. -As an example, based on the data shown in Table 1, the parameter criteria for determining the following are the smoothing conditions of repeating twice the moving average of 50 points taken at a certain time interval from the BS conversion curve. Can be a value (
Table 2).

Mugi 2 The smoothing conditions for the Naori S conversion curve can be determined in such a way that the macroscopic abnormal pattern of the BS curve can be best expressed, so it is not limited to the above example, but can be arbitrarily determined depending on the raw data conditions, for example, the moving average 3 It can be set to repeat twice.

The method for detecting an abnormal pattern of backscattered light in an optical fiber can also be performed mechanically and automatically. That is, as shown in the concept of the system configuration in FIG.
The number of extremely thick and extremely small points obtained as a result and the magnitude of their absolute value are calculated in advance under the same conditions using a computer-based Compan-Y16. By comparing the parameters with reference parameter values obtained from various types of optical fibers, it is possible to automatically and immediately determine the presence or absence of a defect in the optical fiber to be measured and the type of the defect. In this way, it is also possible to provide an automatic optical fiber inspection device.

(1) Effects of the Invention As described above, the present invention converts the BS curve obtained by measuring backscattered light of an optical fiber into a curve indicating the distance from the average straight line to each point on the BS curve, and The curve showing the gap is smoothed, and the number and absolute value of the maximum and minimum points of the curve showing the gap after the smoothing process are used as parameters, and the values are calculated in advance under the same smoothing conditions. The present invention is characterized in that the presence or absence of a defect in the optical fiber and its type are determined by comparing it with a parameter reference value that has been determined.

This provides a method and apparatus for detecting abnormal backscattered light patterns in optical fibers, which makes it possible to accurately and objectively determine the presence or absence of a defect in an optical fiber and its type without visual subjectivity.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the configuration of an optical fiber backscattered light measurement system, Figure 2 is a diagram showing an example of an abnormal pattern of the BS curve of an optical fiber with steps, and Figure 3 is a diagram of an optical fiber with undulations. FIG. 4 is a diagram showing an example of an abnormal pattern of a BS curve of a curved optical fiber; FIG. 5 is a diagram showing an example of a BS curve and its BS conversion curve; Figure 6 shows the curve after smoothing the BS conversion curve in Figure 5 once, Figure 7 shows the curve after smoothing the BS conversion curve in Figure 5 twice, and Figure 8 shows the curve after smoothing the BS conversion curve in Figure 5 twice. Backscattered light abnormality (conceptual diagram of turn detection device. 11... BS curve 14... BS conversion curve 15.
...Falta circuit', 16... Konnok Lake patent applicant Sumitomo Electric Industries, Ltd. Nippon Telegraph and Telephone Public Corporation (5 others) Bong 1 diagram Tora knowledge v! r Ai Qin 57 calculation, 4 Kuni Ira ＼il 1 rod F also electric book 7 I, [temporary burial 6 depression/F

Claims (6)

[Claims] (1) Convert the BS curve obtained by measuring the backscattered light of an optical fiber into a curve that shows the distance from the average straight line to each point on the BS curve, and smooth the curve that shows the distance. death,
The number of maximum points and minimum points of the curve indicating the gap after the smoothing process and their absolute values are used as parameters, and the optical fiber is 1. A method for detecting an abnormal pattern of backscattered light in an optical fiber, the method comprising determining the presence or absence of a defect and its type. (2) The smoothing process is characterized in that the operation of obtaining a moving average of a plurality of points at regular intervals on a curve indicating the gap is repeated once or multiple times. A method for detecting abnormal patterns of backscattered light in optical fibers. (3) The method for detecting an abnormal pattern of backscattered light in an optical fiber according to claim 2, wherein the operation for determining the moving average is repeated twice. (4) BS of optical fiber obtained by optical pulse tester
a filter circuit for smoothing a curve that indicates the distance from the average straight line of the BS curve to each point on the BS curve; a curve obtained by the smoothing process by the filter circuit; A comparator for determining the presence or absence of a defect in the optical fiber and its type by comparing the number of maximum points and minimum points and their absolute values with parameter reference values determined in advance under the same smoothing conditions. An optical fiber backscattered light abnormal pattern detection device comprising: (5) The filter circuit for performing the smoothing process is a one-stage or multi-stage filter circuit for obtaining a moving average of a plurality of points at regular intervals on the curve indicating the gap. An optical fiber backscattered light abnormal pattern detection device according to claim 4. (6) The optical fiber backscattered light abnormal pattern detection device according to claim 5, wherein the plurality of stages of filter circuits are two-stage filter circuits.