JP5493571B2 - OTDR waveform judgment method - Google Patents

Description

  The present invention relates to an OTDR waveform determination method for detecting an abnormal portion having a tilt variation from a measured waveform of an optical fiber measured by an optical pulse tester (hereinafter abbreviated as OTDR) and estimating the cause of the abnormal portion.

Conventionally, a measurement method using an OTDR (abbreviation of Optical Time Domain Reflectometer) has been widely used as a method for measuring a failure point and a break point of a long-distance optical device such as an optical fiber transmission line with a resolution of a meter unit.
In other words, the OTDR measures the return time and the amount of light of backscattered light from each part by inputting a light pulse into the optical fiber under test. Thus, the loss distribution, loss value (loss value), defect position, etc. on the optical fiber under test are calculated. At this time, if there is a portion where the loss is locally high in the optical fiber itself, it appears as a change in inclination on the OTDR waveform. In the inspection process, such a change in inclination is recognized as an abnormal part and appropriately treated.

Such an abnormal part also occurs depending on how the optical fiber is wound during OTDR measurement. Since OTDR measurement is normally performed in a state where it is wound around a bobbin, it is difficult to align and wind well when bobbin is wound. The This is because the increase in the loss due to the optical fiber side pressure and the slight bending occurs in such a line-slipping / meandering portion. Such an OTDR abnormal part due to the winding state disappears by normal rewinding.
On the other hand, although an OTDR abnormal part may occur due to an abnormality caused by the fiber itself, the OTDR abnormal part caused by such a fiber itself does not disappear even if it is wound, and an abnormal part occurs at the same location. It is necessary to identify and remove the abnormal part.

  As an example of a conventional OTDR waveform determination method, when an abnormal portion of an optical fiber is detected using a waveform obtained by OTDR, the effective range is determined by dividing the OTDR waveform into a plurality of sections having a predetermined width. Yes (see, for example, Patent Document 1). Specifically, when the section standard deviation in each section exceeds the threshold and the sections exceeding the threshold continue, the consecutive sections are excluded from the effective range.

JP 2006-64480 A

  However, in the OTDR measurement waveform, although it can be determined whether or not it is an abnormal portion, it is difficult to distinguish between an abnormality caused by winding and another abnormality caused by the optical fiber itself. Therefore, in the case of other abnormalities, although it cannot be corrected even after rewinding, it is necessary to perform rewinding again in the same way as the abnormality caused by winding to check whether an abnormality has occurred at the same location, which is a wasteful process. Had occurred.

  An object of the present invention is to provide an OTDR waveform determination method capable of confirming and selecting an abnormality caused by winding from an OTDR waveform without performing rewinding, in order to solve the above problems.

In order to solve the above-described problem, an OTDR waveform determination method according to the present invention causes test light to enter from one end of an optical fiber wound around a bobbin by using an OTDR measuring device, and return time data and return time data of the return light. Measure the optical power of light, divide the measured OTDR measurement data into a plurality of sections to determine the section loss of each section, and determine the difference between the section loss and the total loss, thereby causing an abnormal part with inclination fluctuation And detecting the increase in loss at the detected abnormal part at each of the determined wavelengths of 1.55 μm or more, obtaining the ratio of the sum of the increase in loss at the abnormal part at each wavelength, and calculating the ratio By detecting the wavelength dependency by comparing with a predetermined value, the detected abnormal portion includes a portion in which the optical fiber is wound without being aligned with the bobbin. Or Is, OTDR waveform judgment method characterized by selecting whether a locally abnormal portion which loss is detected due to that there is a high point on the optical fiber itself.

According to the OTDR waveform determination method configured as described above, the test light is incident from one end of the optical fiber wound around the bobbin using the OTDR measuring device. The return time data of the return light at this time and the optical power data of the return light are measured. Then, the measured OTDR measurement data is divided into a plurality of sections, the section loss of each section is obtained, and the difference between the section loss and the total loss is obtained to detect an abnormal portion (stepped portion, etc.) having a tilt variation. Then, the loss increment at the abnormal part is obtained at each determined wavelength of two or more wavelengths of 1.55 μm or more. Furthermore, the cause of the abnormal part is estimated by calculating the ratio of the sum of the loss increments of the abnormal part at each wavelength and determining the wavelength dependence of the loss increment of the abnormal part by comparing the ratio with a predetermined value. And the detected abnormal portion is an abnormal portion detected because the optical fiber includes a portion wound without being aligned with the bobbin, or the optical fiber itself It is possible to select whether or not an abnormal portion is detected due to the presence of a locally high loss portion . Since abnormalities due to winding can be confirmed and selected from the OTDR waveform, it is not necessary to rewind in the same way in all OTDR abnormal parts, but if there are abnormal parts due to fibers, all abnormal parts are removed. Only when it is determined that is caused by winding, rewinding is sufficient.

  According to the OTDR waveform determination method according to the present invention, it is possible to confirm and select an abnormality caused by winding from an OTDR waveform without performing rewinding.

It is a block diagram which shows the structure of the OTDR measuring apparatus which concerns on this invention. 3 is a flowchart illustrating an embodiment of an OTDR waveform determination method according to the present invention. 5 is a graph showing a relationship between an abnormal amount Δ1550 and an abnormal amount Δ1625 caused by winding in the OTDR waveform determination method according to the present invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of an OTDR waveform determination method according to the present invention will be described in detail with reference to the drawings.

  As shown in FIG. 1, in the OTDR 100, a light source 5 such as a laser diode is excited by a pulse wave of a fixed period generated by a pulse generator 3, and an optical pulse is generated from the light source 5. The light pulse generated by the light source 5 passes through the directional coupler 7 and is incident on one end of an optical fiber 11 to be measured such as a reference optical fiber or an optical fiber to be measured connected via an optical connector 9. It propagates in the optical fiber 11.

  The light pulse that is the return light reflected in the optical fiber 11 to be measured returns to the directional coupler 7 as a backscattered light output, and is sent from the directional coupler 7 to the light receiving unit 13. The light receiving unit 13 includes, for example, an avalanche photodiode (APD) and functions as a photoelectric converter that converts the received backscattered light output into an electric signal. The electric signal converted by the light receiving unit 13 is amplified by an amplifier 15 and then sent to a signal processing device 17. The OTDR characteristics, data, and the like obtained by the signal processing device 17 are stored / stored in the storage device and displayed on the display device 19 such as a liquid crystal display.

  In the OTDR measurement, the slope of the OTDR characteristic represents a loss value, and if there is a turbulence in the optical fiber or an abnormality in the glass itself, the waveform will meander or appear as a step. Thus, by measuring the OTDR characteristic, it is possible to detect an abnormality caused by the winding of the optical fiber and other abnormalities. Note that the OTDR measurement is normally performed in a state of being wound around a bobbin.

Next, the OTDR waveform determination flow will be described with reference to FIG.
The OTDR waveform determination flow includes four steps of OTDR measurement, waveform analysis / abnormal part detection, abnormality amount calculation, and abnormality type determination.

(Measurement fiber OTDR measurement)
The optical fiber 11 to be measured is connected to the directional coupler 7 via the optical connector 9. The signal processing device 17 measures the OTDR characteristic obtained by entering light from one or both ends of the measurement target optical fiber (step S1). The measurement wavelength of OTDR is a light source of a general OTDR and a light source on the long wavelength side. This is because the OTDR anomaly caused by winding appears greatly on the long wavelength side. In the following description, a case where measurement is performed using two wavelengths of 1550 nm and 1625 nm will be described, but the present invention is not limited to this wavelength.
Note that the incident ends of the two wavelengths do not need to be the same (it is only necessary to align the position of the abnormal part later). In the case of both-end incidence, the waveforms incident at both ends of each wavelength are averaged. The next process is advanced later.

(Detection of abnormal part of measurement optical fiber)
Next, an abnormal part (step part) having an inclination variation is detected (step S2). Specifically, the following steps 1) to 6) are performed.

1) The OTDR waveform acquired by OTDR is divided into a plurality of sections.
2) The slope (section loss) within the section is calculated for each section.
3) Determine an effective range for which an abnormal part is detected. The effective range is determined by determining its start point and end point.
4) The inclination of the entire effective range (hereinafter referred to as “total loss”) is obtained.
5) The abnormal part is determined from the effective range. In order to determine the abnormal part, the difference between the total loss and the section loss is obtained. This difference is compared with a predetermined value determined in advance, and it is determined whether or not the section is an abnormal part. That is, if the difference between the total loss and the section loss is greater than or equal to a predetermined value, the section is determined to be an abnormal part. Note that a section in which the standard deviation of the difference between the total loss and the section loss of each section in the effective range is larger than a predetermined value may be determined as an abnormal part.
6) It is determined for all sections whether each section is an abnormal part.

(Abnormal amount calculation of measurement optical fiber)
Next, the section loss measured in the previous process is obtained for each wavelength, and the abnormal amount is calculated (steps S3 to S6).
First, the position of the abnormal part for each wavelength to be compared is matched (step S3). When the abnormal ranges do not completely match at the two wavelengths to be compared (for example, one section is shifted), the section is set to be wide so that both abnormal parts at the two wavelengths are included. The section loss is obtained in units of 1 km and is slid at intervals of 500 m. Therefore, if all section losses within the abnormal range are simply used, overlapping sections will be double counted, so the maximum value of the section loss is determined within the abnormal range (step S4), and the position indicating this maximum value Is used as a starting point, and a section loss is extracted in 1 km steps from the starting point.
In some cases, only 500 m may be included at the end of the abnormal section. In this case, a loss value for 500 m at the end is calculated from the section loss obtained in the 1 km range, and this is used as the abnormal amount at the end. .

(Determination of OTDR abnormal part type)
In the abnormal range obtained in the previous step, the sum of the section losses is obtained for each wavelength while preventing the sections from overlapping as described above (step S5). Thereafter, an abnormal amount (Δ = Σ (section loss−normal loss)) is obtained from the section loss and the normal loss (average loss) within the abnormal range for each wavelength (step S6). In actual calculation, a value obtained by subtracting the normal loss × the number of sections from the total section loss is obtained. Then, the type of the OTDR abnormal part is determined by comparing the ratio of the abnormal amount for each wavelength with the reference value (step S7).

  As described above, according to the OTDR waveform determination method of the present embodiment, an abnormal part having a tilt variation is detected from the measured OTDR measurement data, and the loss increment at the detected abnormal part can be determined to be two or more wavelengths. By obtaining each wavelength and obtaining the wavelength dependence of the loss increment of the abnormal part, the abnormal part due to winding can be selected. Since abnormality due to winding can be confirmed and selected from the OTDR waveform, it is not necessary to rewind in all OTDR abnormal portions, and it is sufficient to rewind only in the case of a fiber including only abnormality due to winding.

  Verification of the above-described OTDR waveform determination method is performed based on a specific calculation example. In addition, the numerical value described below is an example and this invention is not limited to this numerical value.

(Calculation example)
As described above, the section loss is obtained in units of 1 km and 500 m steps. Therefore, the section loss is not simply calculated as Σ (section loss−normal loss) within the abnormal range, and the following method is employed.
1) Detecting a section with a maximum section loss within the abnormal range.
2) Starting from the detected section, skip one section loss so that the sections do not overlap, and obtain the sum of the section losses. However, if the end section loss is only 500 m within the abnormal range, the section loss of 500 m is obtained by weighting in consideration of the preceding and following section loss.
3) The normal loss is subtracted from the sum of the section losses obtained in 2) to obtain the abnormal amount.

In Table 1, the range of 33 km to 35.5 km was determined as an abnormal interval at a wavelength of 1550 nm, and the range of 33 km to 36 km was determined as an abnormal interval at a wavelength of 1625 nm.
Since the abnormal range is different between the wavelength 1550 nm and the wavelength 1625 nm, matching is performed, and the range of 33 km to 36 km is set as the abnormal range in accordance with the wavelength 1625 nm having a wide abnormal range.

Find the maximum section loss within the abnormal range of 1) above.
According to Table 1, 34.5 to 35.5 km indicating 0.19882 (★ mark) at section loss @ 1550 nm, and 33.5 to 34.5 km indicating 0.25385 (★ mark) at section loss @ 1625 nm. It becomes section loss.

The sum of the section losses is calculated from the section that is the starting point of 2).
The range (end) of section loss (33.0-34.0) to 33.0-33.5, section loss (33.5-34.5), section loss (34.5-35.5), Sum of sections (ends) ranging from section loss (35.0 to 36.0) to 35.5 to 36.0 (sum of slanted sections within the thick frame in Table 1. Section including ends Is only the value calculated for 0.5 km where the ranges do not overlap. Note that, as a method of extracting only the 500 m portion from the end section, weighted averaging with a section in which sections to be excluded overlap is performed. That is, it is obtained from the following equation.
Section loss (33.0 to 33.5) = section loss (33.0 to 34.0) × {section loss (33.0 to 34.0) / (section loss (33.0 to 34.0) + Section loss (33.5-34.5))}

The calculation result of the sum of the section loss is as follows.
The sum of the wavelengths of 1550 nm is Σ section loss (33.0-36.0) = 0.19126 ×
0.19126 / (0.19126 + 0.19267)
+0.19267
+0.19882
+ 0.18442 × 0.18442 / (0.19882 + 0.18442)
= 0.575514 dB
The sum total of the wavelength 1625 nm is Σ section loss (33.0-36.0) = 0.282854 ×
0.22854 / (0.22854 + 0.25385)
+0.25385
+0.22729
+ 0.21377 × 0.21377 / (0.22729 + 0.21377)
= 0.693023dB

The abnormal amount (Δ) of 3) is calculated by subtracting (normal loss × number of abnormal ranges) from the sum of the section losses in the abnormal range obtained in 2). The normal loss is a measured value (average value) of the entire OTDR.
Δ1550 = 0.575514-0.186 × 3 = 0.0175514 dB
Δ1625 = 0.6930303-0.212 × 3 = 0.057023 dB
Loss increment ratio Δ1550 / Δ1625 = 0.307

FIG. 3 shows the relationship between the abnormal amount Δ1550 due to winding and the abnormal amount Δ1625. From the graph, it can be seen that when the abnormal amount due to winding is graphed in this way, it is on a straight line with a certain slope. This straight line can be expressed by the following equation where y is the abnormal amount Δ1550 and x is the abnormal amount Δ1625.
y = 0.3652x
In general, in the case of an OTDR abnormality other than that due to winding, since the wavelength dependency is small, the value of Δ1550 / Δ1625 increases. That is, by calculating this ratio and comparing it with a reference value, it is possible to determine whether the abnormality is due to winding or other abnormality. In the above example, if the reference value of Δ1550 / Δ1625 is set to 0.4, for example, it can be determined that the value is greater than this, except for winding, and if it is less than this, it is determined that winding is caused.

3 Pulse generator 5 Light source (laser diode)
7 Directional coupler 9 Optical connector 13 Light receiving part (photoelectric converter)
15 Amplifier
17 Signal Processing Device 19 Display Device 100 OTDR (Optical Pulse Tester)

Claims (1)

The test light is incident from one end of the optical fiber wound in the bobbin by the OTDR measuring instrument, the return time data of the return light and the optical power of the return light are measured, and the measured OTDR measurement data Dividing into sections to determine section loss of each section, and detecting the difference between the section loss and the total loss to detect an abnormal part with inclination fluctuation, and increase the loss increment at the detected abnormal part to 1.55 μm or more It was detected at each determined wavelength of two or more wavelengths, and the ratio of the total loss increment of the abnormal portion at each wavelength was determined, and the wavelength dependency was determined by comparing the ratio with a predetermined value . The abnormal portion is an abnormal portion detected because the optical fiber includes a portion wound without being aligned with the bobbin , or a location where the optical fiber itself has a high loss Wake up to OTDR waveform judgment method characterized by selecting whether the detected abnormal portion by.

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