JP7548321B2 - Apparatus and method for detecting trends in microbending loss in optical fiber - Google Patents

Description

Regarding the maintenance and operation of optical fiber.

When water penetrates the coating of an optical fiber, microbends can occur. This is important in maintaining optical fiber, especially since the increase in microbend loss due to immersion changes gradually. Methods for detecting loss due to microbends include measuring transmission loss using an OTDR (Optical Time Domain Reflectometer) and optical loss using an optical power meter.

Hirofumi Amano, "All about Access Networks", p. 52, Telecommunications Association, July 1, 2017. Hiroshi Takahashi et al., "Branch Optical Fiber Loss Measurement Technology Enabling End-to-End Measurement of Optical Access Lines," NTT Technical Journal, December 2017, pp. 58-62.

However, microbending loss can show a tendency to decrease after increasing once, and with detection using loss, if there is no data on the change in loss over time, it is not possible to know the increase or decrease in microbending loss when measuring loss. For this reason, with detection using loss alone, optical fiber transmission loss may show a decreasing trend, and repair operations may be required for optical fiber failures even though there is no problem with service operation from the perspective of transmission loss.

Therefore, the present disclosure aims to detect the increase/decrease trend of microbending loss in optical fiber in which microbending occurs, without requiring data on changes over time, in order to reduce unnecessary optical fiber failure repair operations.

The apparatus according to the present disclosure comprises:
Measure the forward Brillouin scattering (GAWBS) of the test optical fiber in which the microbend of interest occurs;
An increase or decrease tendency of the microbending loss of the optical fiber under test is detected based on the characteristics around the peak of the forward Brillouin scattering.

The method according to the present disclosure comprises:
Measure the forward Brillouin scattering of the test optical fiber in which the microbend of interest occurs;
An increase or decrease tendency of the microbending loss of the optical fiber under test is detected based on the characteristics around the peak of the forward Brillouin scattering.

This disclosure makes it possible to detect the increase or decrease in microbending loss in optical fiber where a microbend has occurred on the spot, even when there is no data on changes over time. This makes it possible to reduce unnecessary repair operations using optical fiber due to microbending loss.

1A and 1B are examples of GAWBS, where (a) shows a depolarized GAWBS and (b) shows a polarized GAWBS. 1 shows an example of a spectrum waveform of GAWBS. 1 shows a close-up of one of the peaks in the GAWBS spectral waveform. An example of the change over time of GAWBS is shown. 1 illustrates a first system configuration example according to a first embodiment. 2 illustrates a second system configuration example according to the first embodiment. 13 illustrates a third system configuration example according to the first embodiment. 1 shows an example of a method for detecting a trend of increase or decrease in microbending loss according to a first embodiment. 1 shows a first system configuration example according to a second embodiment. 13 illustrates a second system configuration example according to the second embodiment. 13 illustrates a third system configuration example according to the second embodiment. 13 shows a first example of a method for detecting an increase/decrease trend of microbending loss according to the second embodiment. 13 shows a second example of the method for detecting an increase/decrease trend of microbending loss according to the second embodiment. 13 shows a third example of the method for detecting an increase/decrease trend of microbending loss according to the second embodiment.

Below, the embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below. These implementation examples are merely illustrative, and the present disclosure can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art. Note that components with the same reference numerals in this specification and drawings are considered to be identical to each other.

<Principle>
FIG. 1 shows an example of GAWBS (Guided acoustic-wave Brillouin scattering). When light is incident on an optical fiber, heat is generated due to light absorption in the core of the optical fiber, and sound waves are generated accordingly. GAWBS is a phenomenon in which the polarization and phase of light propagating within the optical fiber are modulated by sound waves propagating while reflecting in the radial direction of the optical fiber. The spectrum of GAWBS depends on the propagation loss of the sound waves, the main factor being the reflectance of the sound waves. The reflectance of the sound waves within the optical fiber is affected by the acoustic impedance outside the optical fiber. The acoustic impedance of the optical fiber changes according to changes in the coating of the optical fiber.

It is believed that the state of the coating of an optical fiber in which a microbend occurs changes, and as the coating changes, the acoustic impedance also changes, causing a change in the GAWBS spectrum. For example, if the acoustic impedance outside the optical fiber decreases and the reflectivity of sound waves inside the optical fiber increases, the half-width of the peak in the GAWBS spectrum decreases. This disclosure uses this change to detect the increase or decrease in microbending loss in an optical fiber in which a microbend occurs.

Figure 2 shows an example of a GAWBS spectral waveform. Figure 3 shows an enlarged view of one of the peaks in the GAWBS spectral waveform. It can be seen that the spectrum changes as the transmission loss increases due to the occurrence of microbends. Therefore, the present disclosure detects changes in the condition of the optical fiber coating using any combination of changes in the forward Brillouin scattering (GAWBS) spectrum as shown below.

3, the microbending loss increases once and then decreases, but the intensity of the frequency of the peak in the GAWBS spectrum remains large even after the microbending loss starts to decrease. The present disclosure may employ an embodiment in which the intensity of the frequency of the peak in the GAWBS spectrum is observed, and the increase/decrease trend of the microbending loss is detected from the magnitude of the intensity, utilizing the fact that the intensity remains large even after the microbending loss decreases.

- GAWBS Spectral Linewidth As shown in FIG. 3, the microbending loss increases once and then decreases, but the GAWBS spectral linewidth narrows even after the microbending loss starts to decrease. The present disclosure may employ an aspect in which the narrowing of the GAWBS spectral linewidth is utilized to detect the increase/decrease trend of the microbending loss from the narrowing of the linewidth. The linewidth can be calculated by approximating the spectrum with a Lorentz curve. Approximation with a Lorentz curve is calculated, for example, by fitting the periphery of each peak of the spectrum with a Lorentz curve.

-Spectral kurtosis of GAWBS As shown in FIG. 3, as the line width of the spectrum narrows, the kurtosis of the spectrum increases. Kurtosis is how sharp a spectrum is compared to a normal distribution. Therefore, the present disclosure may employ an aspect in which the kurtosis of the spectrum is observed, and the increase in the kurtosis is utilized to detect the increase or decrease in the microbends based on the magnitude of the kurtosis. For example, the kurtosis of the spectrum can be calculated by the following formula. Here, the sample size is n, the average value of each data x i (i: 1, 2, ..., n) is x, and the sample standard deviation is s.

Figure 4 shows an example of the change over time of GAWBS. Each frequency is a frequency at which a peak exists in the spectrum of GAWBS. The half-width of the peak in the 108 MHz band at the start of the immersion test when no microbends have occurred is 0.768 MHz, and the half-width of the peak at 13.36 hours after the start of the immersion test when the loss due to microbends has increased is 0.366 MHz. In contrast, the half-width of the peak at 270.16 hours after the start of the immersion test when the loss due to microbends has decreased is 0.278 MHz. After the occurrence of microbends, the transmission loss increases and then gradually decreases. On the other hand, the half-width of the peak in the spectrum of GAWBS is narrowed, and the increase/decrease trend of the transmission loss can be understood by using the half-width. For example, in the case of the optical fiber shown in Fig. 4, if the measurement result by OTDR is a transmission loss of 0.522 dB/km and the half-width of the GAWBS is 0.395 MHz, it is understood that the transmission loss will increase in the future. On the other hand, if the half-width of the GAWBS is 0.315 MHz, it is understood that the transmission loss will decrease in the future. In this way, by using the change in the waveform of the GAWBS spectrum, it is possible to detect the increase or decrease trend of the microbending loss.

<Measurement method>
The change in the spectrum of GAWBS caused by microbending occurs regardless of the presence or absence of polarization. Therefore, there are polarized GAWBS and depolarized GAWBS, and either one can be used.

In addition, there are multiple peaks in the GAWBS spectrum, and any peak may be used. However, among the multiple peaks, the low-frequency peaks also include GAWBS between the coating and the external environment. In order to increase the efficiency of detecting microbending loss, it is preferable to have less GAWBS between the coating and the external environment. Therefore, a peak of a certain degree of high frequency that has less GAWBS between the coating and the external environment among the multiple peaks is desirable. On the other hand, it is desirable to make the judgment using a frequency with the greatest intensity at the spectral peak, such as using the peak with the greatest intensity.

The GAWBS spectrum can be measured using a spectrum analyzer or a Fourier transform of the oscilloscope waveform. The GAWBS spectrum can also be measured using the Brillouin gain spectrum. The GAWBS spectrum can also be measured by cutting out the frequency band in which the peak appears using a filter, which speeds up signal processing. It is also desirable to perform averaging processing on the spectrum to reduce measurement noise.

First Embodiment
5 to 7 show system configuration examples according to the present disclosure. A microbending loss increase/decrease trend detection device 10 according to the present disclosure is disposed in a base station 91 and connected to a measured optical fiber 95. In a first system configuration example shown in Fig. 5 and a second system configuration example shown in Fig. 6, both ends of the measured optical fiber 95 are connected to the microbending loss increase/decrease trend detection device 10. In a third system configuration example shown in Fig. 7, one end of the measured optical fiber 95 is connected to the microbending loss increase/decrease trend detection device 10.

The microbending loss increase/decrease trend detection device 10 includes a light source 11, a detector 12, and an analyzer/display 13, and measures the spectrum of the GAWBS. The light source 11 emits test light to the optical fiber 95 under test. The wavelength of the test light is arbitrary. When a working line is used for the optical fiber 95 under test, the wavelength of 1650 nm, which is the test wavelength of the actual network, is used as the wavelength of the test light. The detector 12 detects the scattered light of the test light scattered by the optical fiber 95 under test through a polarizer. The analyzer/display 13 measures the GAWBS using the scattered light detected by the detector 12. The analyzer/display 13 then uses the spectrum to detect the increase/decrease trend of the microbending loss of the optical fiber 95 under test. The increase/decrease trend of the microbending loss is determined using the linewidth of the GAWBS spectrum and the intensity of the frequency of the peak of the GAWBS spectrum, as explained in the principle.

The analysis/display unit 13 in the microbend loss increase/decrease trend detection device 10 disclosed herein can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided via a network.

In the second system configuration example shown in Figure 6, the microbend loss increase/decrease trend detection device 10 is equipped with a coupler 14 to form a Sagnac loop. As shown in Figure 6, the present disclosure can employ a general polarized GAWBS measurement system.

In the third system configuration example shown in Figure 7, the microbending loss increase/decrease trend detection device 10 includes a circulator 15. The circulator 15 directs light from the light source 11 into the measured optical fiber 95 and emits the scattered light in the measured optical fiber 95 to the detector 12. The scattered light scattered in the measured optical fiber 95 is detected through a polarizer.

When measuring the distance distribution, results like those shown in Figure 3 are obtained at each point along the length of the cable. By comparing the results obtained at each point with a threshold, it is possible to identify the point where a trend in microbending loss increases or decreases was detected, and to identify the distance from the microbending loss increase or decrease trend detection device 10. By using a database that manages the distance from the microbending loss increase or decrease trend detection device 10 to each cable and the installation location of each cable, it is possible to identify the installation location of the cable where a trend in microbending loss increases or decreases was detected.

Figure 8 shows an example of a method for detecting an increase or decrease in microbend loss according to this embodiment. The microbend detection method according to this embodiment includes a GAWBS measurement step S101, a line width calculation step S102, a threshold comparison step S103, a microbend loss increase trend detection step S104, and a microbend loss decrease trend detection step S105.

In the GAWBS measurement procedure S101, the light source 11, the detector 12, and the analyzer/display unit 13 measure the GAWBS.
In the linewidth calculation step S102, the analyzer and display unit 13 calculates the linewidth of the GAWBS spectrum.
In the threshold comparison step S103, the linewidth of the GAWBS spectrum is compared with a predetermined threshold. If the linewidth of the GAWBS spectrum is equal to or greater than the predetermined threshold, the analyzer/display unit 13 determines that the microbending loss in the measured optical fiber 95 is on an increasing trend (S104). If the linewidth of the GAWBS spectrum is less than the predetermined threshold, the analyzer/display unit 13 determines that the microbending loss in the measured optical fiber 95 is on a decreasing trend (S105).
In the microbending loss increasing trend detection step S104, the analyzer/display unit 13 displays that the microbending loss of the test optical fiber 95 is in an increasing state.
In the microbending loss decreasing trend detection step S105, the analyzer and display unit 13 displays that the microbending loss of the measured optical fiber 95 is in a decreasing trend state. At this time, the analyzer and display unit 13 may transmit an alarm to a predetermined address.

In this embodiment, an example of executing the linewidth calculation procedure S102 using the linewidth of the spectrum has been shown, but any detection method using the spectrum can be used. For example, the linewidth calculation procedure S102 may be a procedure of calculating the intensity of the peak frequency, or a procedure of calculating the kurtosis of the spectrum. In this case, in the threshold comparison procedure S103, if the difference is equal to or less than a predetermined threshold, the analyzer/display unit 13 determines that the microbending loss in the measured optical fiber 95 is on an increasing trend (S104). If the difference is equal to or more than the predetermined threshold, the analyzer/display unit 13 determines that the microbending loss in the measured optical fiber 95 is on a decreasing trend (S105).

As described above, the microbending loss increase/decrease trend detection device 10 of this embodiment can detect the increase/decrease trend of the microbending loss of the measured optical fiber 95 in which a microbend is occurring. Here, by using the change in the spectral waveform of the GAWBS, the increase/decrease trend of the transmission loss can be detected without measuring the change over time. Therefore, the present disclosure can determine whether the microbending loss of the measured optical fiber will affect services in the future. Furthermore, it is believed that the device can also be used to detect microbending caused by conditions other than immersion, such as high temperature and high humidity.

Second Embodiment
9 to 11 show an example of a system configuration according to the present disclosure. In the embodiment of FIG. 9, the OTDR 51 outputs pulsed light to the measured optical fiber 95 and outputs return light from the measured optical fiber 95. In the detector 12, the return light from the OTDR 51 may be converted from GAWBS modulation to light intensity modulation using a polarizer, or an SSB (single side-band) modulator may be used to cause interference between the return light and light from another light source and convert the GAWBS modulation to light intensity modulation. When using an SSB modulator, it is preferable to use the OTDR 51 as the light source in order to reduce measurement noise caused by the light source. The analyzer/display unit 13 measures the signal received by the detector 12 with an oscilloscope, and measures at each frequency while sweeping the frequency with an arbitrary waveform generator, thereby making it possible to measure the distance distribution of the GAWBS spectrum.

In the embodiment shown in FIG. 10, the distance distribution of GAWBS can be measured using a BOTDR (Brillouin Optical Time Domain Reflectometer). The BOTDR 52 outputs pulsed light to the optical fiber 95 under test, and outputs the Brillouin scattering spectrum measured from the return light of the Brillouin scattering modulated by the GAWBS from the optical fiber 95 under test. The analyzer/display 13 subtracts the peak frequency (Brillouin frequency shift) of the Brillouin scattering spectrum from the Brillouin scattering spectrum measured by the BOTDR 52 to measure the GAWBS spectrum.

In the embodiment shown in FIG. 11, the distance distribution of GAWBS can be measured using BOTDA (Brillouin Optical Time Domain Analysis). BOTDA 53 outputs pulsed light and continuous light to the optical fiber 95 under test, and outputs a Brillouin scattering spectrum that measures the gain or loss due to the Brillouin scattering light modulated by GAWBS from the optical fiber 95 under test. The analyzer/display 13 subtracts the peak frequency (Brillouin frequency shift) of the Brillouin scattering spectrum from the Brillouin scattering spectrum measured by BOTDA 53 to measure the GAWBS spectrum.

Figure 12 shows a first example of the method for detecting a trend of increase or decrease in microbends according to this embodiment. The method for detecting a trend of increase or decrease in microbends according to this embodiment includes a temperature measurement step S111 before the GAWBS measurement step S101, and a temperature correction step S112 between the line width calculation step S102 and the threshold comparison step S103.

In temperature measurement S111, as in the form of Figure 10, a BOTDR or ROTDR (Raman Optical Time Domain Reflectometry) measures Brillouin scattering or Raman scattering in the measured optical fiber 95, and the analyzer/display unit 13 uses the Brillouin scattering spectrum or Raman scattering spectrum to measure the distance distribution of temperature in the measured optical fiber 95. Alternatively, as in the form of Figure 11, a BOTDR may measure the gain or loss due to Brillouin scattering in the measured optical fiber 95, and the analyzer/display unit 13 may use the Brillouin scattering spectrum to measure the distance distribution of temperature in the measured optical fiber 95.

In the temperature correction step S112, the analysis/display unit 13 corrects the line width calculated in the line width calculation step S102 using the temperature in the measured optical fiber 95.

Figure 13 shows a second example of the microbend increase/decrease trend detection method of this embodiment. The microbend increase/decrease trend detection method of this embodiment includes a stress measurement step S121 before the GAWBS measurement step S101, and a stress correction step S122 between the line width calculation step S102 and the threshold comparison step S103.

In the stress measurement procedure S121, the BOTDR 52 measures the Brillouin scattering in the measured optical fiber 95 as in the embodiment of Fig. 10, and the analyzer/display unit 13 uses the Brillouin scattering spectrum to measure the distance distribution of the stress in the measured optical fiber 95. Alternatively, as in the embodiment of Fig. 11, the BOTDR 53 may measure the gain or loss due to Brillouin scattering in the measured optical fiber 95, and the analyzer/display unit 13 may use the Brillouin scattering spectrum to measure the distance distribution of the stress in the measured optical fiber 95.
In the stress correction step S122, the analyzer/display unit 13 corrects the line width calculated in the line width calculation step S102 using the stress in the optical fiber 95 to be measured.

Figure 14 shows a third example of the microbend increase/decrease trend detection method of this embodiment. The microbend increase/decrease trend detection method of this embodiment includes a temperature and stress measurement step S131 before the GAWBS measurement step S101, and a temperature and stress correction step S132 between the line width calculation step S102 and the threshold comparison step S103.

In the temperature and stress measurement procedure S131, the BOTDR 52 measures the Brillouin scattering in the measured optical fiber 95 as in the configuration of Figure 10, and the analyzer/display 13 measures the distance distribution of the stress in the measured optical fiber 95 using the Brillouin scattering spectrum. Alternatively, as in the configuration of Figure 11, the BOTDR 53 may measure the gain or loss due to Brillouin scattering in the measured optical fiber 95, and the analyzer/display 13 may measure the distance distribution of the stress in the measured optical fiber 95 using the Brillouin scattering spectrum. Alternatively, as in the configuration of Figure 10, the ROTDR measures the Raman scattering in the measured optical fiber 95, and the analyzer/display 13 measures the distance distribution of the temperature in the measured optical fiber 95 using the Raman scattering spectrum.

In the temperature and stress correction procedure S132, the analysis/display unit 13 corrects the line width calculated in the line width calculation procedure S102 using the temperature and stress of the measured optical fiber 95.

The line width and kurtosis of the GAWBS are linearly related to the acoustic impedance of the coating, and the acoustic impedance changes linearly with temperature and stress. Furthermore, the strength of the GAWBS changes accordingly when the line width changes. In other words, the GAWBS is linearly related to temperature and stress. Therefore, the analyzer/display unit 13 can detect temperature and stress changes using the distance distribution of the measured temperature and stress, and correct the GAWBS.

In this embodiment, an example is shown in which the line width calculation procedure S102 using the line width of the spectrum is executed to correct the line width, but the method can be applied to any detection method using a spectrum and its correction. For example, the line width calculation procedure S102 may be a procedure for calculating the intensity of the peak frequency. In this case, the intensity of the peak frequency is corrected in steps S112, S122, and S132.

This disclosure can be applied to the information and communications industry.

10: Microbend loss increase/decrease trend detection device 11: Light source 12: Detector 13: Analysis/display device 14: Coupler 15: Circulator 21, 22, 23: Closure 51: OTDR
52: BOTDR
53: BOTDA
91: Base station 92, 93, 94: Manhole 95: Optical fiber to be measured

Claims (5)

Measure the forward Brillouin scattering of the test optical fiber in which the microbend of interest occurs;
detecting an increase or decrease in microbending loss of the test optical fiber when the test optical fiber is continuously immersed in water based on characteristics around the peak of the forward Brillouin scattering;
Device. The characteristic is at least one of the intensity, linewidth, and kurtosis of at least one peak included in the forward Brillouin scattering.
2. The apparatus of claim 1. Further comprising an OTDR for measuring one or both of the temperature and the stress of the test optical fiber;
correcting said characteristics using the measured temperature and stress;
3. Apparatus according to any one of claims 1 to 2. The apparatus measures forward Brillouin scattering of a test optical fiber in which a microbend of interest occurs;
The device detects an increase or decrease in microbending loss of the test optical fiber when the test optical fiber is continuously immersed in water based on characteristics around the peak of the forward Brillouin scattering.
method. the apparatus further measures one or both of a temperature and a stress of the test optical fiber;
The device corrects the characteristics using the results of the measurements.
The method according to claim 4.

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