CN215871418U

CN215871418U - Optical cable anomaly detection system

Info

Publication number: CN215871418U
Application number: CN202121625850.2U
Authority: CN
Inventors: 孙少华; 杨林慧; 刘永胜; 长全平
Original assignee: State Grid Corp of China SGCC; State Grid Qinghai Electric Power Co Ltd; Information and Telecommunication Branch of State Grid Qinghai Electric Power Co Ltd
Current assignee: State Grid Corp of China SGCC; State Grid Qinghai Electric Power Co Ltd; Information and Telecommunication Branch of State Grid Qinghai Electric Power Co Ltd
Priority date: 2021-07-16
Filing date: 2021-07-16
Publication date: 2022-02-18
Anticipated expiration: 2031-07-16

Abstract

The utility model discloses an optical cable abnormity detection system. Wherein, include: the optical time domain reflectometer is connected with the controller, and the output end of the optical time domain reflectometer is connected with one end of the monitored target optical cable and is used for transmitting a detection signal to the target optical cable and receiving a feedback signal of the target optical cable for reflecting the detection signal; the controller comprises a sampling module, a statistical module, a wavelet transform module and an analysis module; the sampling module is connected with the output end of the optical time domain reflectometer; the statistical module is connected with the sampling module, and the wavelet transformation module is connected with the statistical module; the analysis module is connected with the wavelet transformation module. The utility model solves the technical problem that the optical cable fault detection in the related technology is not comprehensive and accurate enough.

Description

Optical cable anomaly detection system

Technical Field

The utility model relates to optical cable detection, in particular to an optical cable abnormity detection system.

Background

With the rapid development of optical fiber networks, the complexity of the networks is increasing, and the management and maintenance work of optical fiber physical networks is heavy. The key point of the current network maintenance is to find the fault of the optical fiber network in time and ensure the safety and stability of the optical fiber physical network. Therefore, an optical fiber monitoring system is urgently needed to be established, and optical fiber monitoring, warning, fault analysis, positioning, line maintenance and the like are organically combined together, so that guarantee is provided for safe and efficient operation of an optical fiber network.

The primary detection purposes of fiber monitoring are to detect the location of singularities or faults in the fiber and the attenuation characteristics of the fiber. Methods for measuring attenuation are mainly truncation, interpolation and retro-reflection. The truncation method is to measure the optical power passing through two cross sections of the optical fiber without changing the injection conditions, thereby directly obtaining the attenuation value of the optical fiber. The insertion loss method is similar to the truncation method in principle, but the optical power at the injection end of the optical fiber is the optical power injected into the output end of the system, the measured attenuation of the optical fiber comprises the attenuation of an experimental device, and the measured result must be corrected by the loss of an additional connector and the loss of a reference optical fiber section respectively.

At present, most of communication operators and management departments mainly adopt the traditional means of ITU-T recommendation to maintain and manage the optical cable network, namely, the condition of the optical fiber is detected by monitoring the condition of the transmission error rate. The method comprises the steps of firstly setting a threshold value, comparing the error rate with the threshold value, temporarily closing the optical fiber detection system once the error rate exceeds the threshold value, then judging fault information, and firstly judging whether the optical cable network has a fault or the transmission equipment has a fault. If the optical cable network has a problem and a fault occurs, the optical cable network is detected through OTDR equipment, a specified optical cable section is tested, and finally, a professional carries out manual analysis on a test curve returned by the OTDR equipment test, so that fault information is judged, and the position of a fault point is determined.

The manual detection of the OTDR curve is determined by the experience of maintenance personnel, and usually, whether the optical cable line is damaged is patrolled on the optical cable line, if the optical cable line has no obvious damage sign, great difficulty is caused to the maintenance personnel to find out a fault point, and sometimes even a splice closure needs to be dug out for testing to further determine the approximate position of the fault point. This results in a large amount of inefficient work, which is not as difficult to find a fault as rewiring over a section of area if a complex topographical environment is encountered.

And a searching method for accurate positioning cannot be established, so that the accuracy rate of optical cable fault detection is low.

In view of the above problems, no effective solution has been proposed.

SUMMERY OF THE UTILITY MODEL

The embodiment of the utility model provides an optical cable abnormity detection system, which at least solves the technical problem that optical cable fault detection in the related technology is not comprehensive and accurate enough.

According to an aspect of an embodiment of the present invention, there is provided an optical cable abnormality detection system including: the optical time domain reflectometer is connected with the controller, and the output end of the optical time domain reflectometer is connected with one end of a monitored target optical cable and is used for transmitting a detection signal to the target optical cable and receiving a feedback signal of the target optical cable reflecting the detection signal; the controller comprises a sampling module, a statistical module, a wavelet transformation module and an analysis module; the sampling module is connected with the output end of the optical time domain reflectometer and is used for sampling the feedback signals according to a preset time interval to obtain feedback signals at multiple moments; the statistical module is connected with the sampling module and used for performing statistics on the feedback signals at multiple moments to generate corresponding optical power curves, and the wavelet transformation module is connected with the statistical module and used for performing wavelet transformation on the optical power curves to generate attenuation curves; and the analysis module is connected with the wavelet transformation module and used for analyzing the attenuation curve through an analysis method and determining the position of the target optical cable with abnormality.

Optionally, the wavelength of the detection signal output by the output end of the optical time domain reflectometer is greater than a wavelength threshold, and the wavelength threshold is 1300nm to 1700 nm.

Optionally, the optical time domain reflectometer includes a pulse generator, a coupler, and a light detector, where the pulse generator is connected to an input/output end of the coupler, an output end of the coupler is connected to a section of a target optical cable to be monitored, and an end of the target optical cable connected to the coupler is also connected to the light detector; the optical time domain reflectometer further comprises: and the driver is connected with the pulse generator and is used for driving the pulse generator to work.

Optionally, the coupler includes a modulation device, an amplification device and a polarization disturbing device, an input end of the modulation device is connected to an output end of the pulse generator, an output end of the modulation device is connected to an input end of the amplification device, an output end of the amplification device is connected to an input end of the polarization disturbing device, and an output end of the polarization disturbing device is connected to the target optical cable; the modulation device and the deflection disturbing device are both connected with the driver.

Optionally, the optical time domain reflectometer further includes: the control device, the signal processing device and the output interface; the control device is connected with the input end of the driver; the signal processing device comprises a digital-to-analog converter, a digital frequency converter and a digital signal processor; the input end of the digital-to-analog converter is connected with the control device and the output end of the receiver, and the input end of the receiver is connected with the target optical cable; the output end of the digital-to-analog converter is connected with the input end of the digital frequency converter, the input end of the digital signal processor is connected with the output end of the digital frequency converter, and the digital signal processor is connected with the output interface.

Optionally, the wavelet transform module includes: the decomposition unit is connected with the statistic module and used for performing wavelet decomposition on the power curve to determine a wavelet coefficient; and the reconstruction unit is connected with the decomposition unit and used for reconstructing the power curve according to the wavelet coefficient through a reconstruction algorithm to determine the attenuation curve.

Optionally, the decomposition unit includes: the decomposition subunit is connected with the reconstruction unit and used for decomposing the power curve according to the wavelet basis function and the decomposition layer number to obtain multilayer decomposition signals, wherein each layer of decomposition signals comprises a high-frequency part and a low-frequency part of a previous layer of signals; the first determining subunit is connected with the decomposing subunit and used for determining the high-frequency coefficient of each layer of decomposed signal according to the high-frequency part of each layer of decomposed signal; and the second determining subunit is connected with the first determining subunit and used for determining the wavelet coefficients according to the high-frequency coefficients of the multilayer decomposition signals.

Optionally, the analysis module includes: the searching unit is connected with the reconstruction unit and used for searching and positioning the attenuation curve according to a preset amplitude threshold value; and the positioning unit is connected with the searching unit and used for determining the position of the target optical cable corresponding to the amplitude value under the condition that the amplitude value of the attenuation curve reaches the preset amplitude value threshold value, and the abnormal condition of the reflection event occurs.

Optionally, the analysis module further comprises: the preliminary positioning unit is connected with the reconstruction unit and used for searching the attenuation curve according to the waveness characteristics of the non-reflection event faults and determining a plurality of preliminary positioning points of the non-reflection event faults on the attenuation curve; the secondary positioning unit is connected with the primary positioning unit and used for determining the primary positioning point with attenuation reaching a preset attenuation threshold value as a normal starting point according to the attenuation of the plurality of primary positioning points; and the final positioning unit is connected with the re-positioning unit and used for determining an amplitude difference according to the curve amplitude of the position of the preset distance before and after the normal starting point, and determining that the position of the target optical cable corresponding to the normal starting point is abnormal in a non-reflection event under the condition that the amplitude difference reaches a preset difference value.

Optionally, the abnormality of the reflection event includes at least one of: the peak value of the reflection peak is saturated; secondary reflection; negative loss; the anomaly of the non-reflection event includes at least one of: a special breakpoint; cracking the optical cable; and source end breakpoints.

In the embodiment of the utility model, an optical time domain reflectometer and a controller are adopted, the optical time domain reflectometer is connected with the controller, and the output end of the optical time domain reflectometer is connected with one end of a target optical cable to be monitored and used for transmitting a detection signal to the target optical cable and receiving a feedback signal of the target optical cable for reflecting the detection signal; the controller comprises a sampling module, a statistical module, a wavelet transform module and an analysis module; the sampling module is connected with the output end of the optical time domain reflectometer and is used for sampling the feedback signals according to a preset time interval to obtain feedback signals at a plurality of moments; the statistical module is connected with the sampling module and used for performing statistics on the feedback signals at a plurality of moments to generate corresponding optical power curves, and the wavelet transformation module is connected with the statistical module and used for performing wavelet transformation on the optical power curves to generate attenuation curves; the analysis module is connected with the wavelet transformation module and used for analyzing the attenuation curve through an analysis method and determining the abnormal position of the target optical cable, performing wavelet transformation on the power curve according to the power curve of the feedback signal reflected by the target optical cable detected by the optical time domain reflectometer to obtain the attenuation curve, and determining the abnormal event and the abnormal position according to the attenuation curve, so that the purpose of analyzing the attenuation curve obtained through the wavelet transformation of the feedback signal and effectively determining the abnormal event and the abnormal position is achieved, the technical effect of improving the accuracy of optical cable abnormality detection is achieved, and the technical problem that optical cable fault detection in the related technology is not comprehensive and accurate enough is solved.

Drawings

The accompanying drawings, which are included to provide a further understanding of the utility model and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the utility model and together with the description serve to explain the utility model without limiting the utility model. In the drawings:

FIG. 1 is a schematic view of a cable anomaly detection system according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of a COTDR system architecture according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of a light source module according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of a modulation module according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of a deflection module according to an embodiment of the present invention;

FIG. 6 is a schematic diagram of a balanced detection module according to an embodiment of the utility model;

FIG. 7 is a schematic diagram of an analog-to-digital conversion module according to an embodiment of the utility model;

FIG. 8 is a schematic diagram of a digital down conversion module according to an embodiment of the present invention;

FIG. 9 is a schematic diagram of a digital signal processing module according to an embodiment of the present invention;

FIG. 10 is a schematic diagram of a 5-tap FIR filter according to an embodiment of the present invention;

FIG. 11 is a schematic diagram of a drive control module according to an embodiment of the present invention;

FIG. 12-1 is a schematic diagram of a laser modulation circuit according to an embodiment of the present invention;

FIG. 12-2 is a schematic diagram of an acousto-optic modulator modulation circuit according to an embodiment of the utility model;

FIG. 12-3 is a schematic diagram of a scrambler drive circuit according to an embodiment of the present invention;

FIG. 13 is a schematic diagram of a control module according to an embodiment of the present invention;

FIG. 14-1 is a schematic diagram of an OTDR test curve according to an embodiment of the present invention;

FIG. 14-2 is a schematic illustration of the test curve of FIG. 14-1 after Gabor transform analysis;

FIG. 14-3 is a schematic illustration of the test curve of FIG. 14-1 after wavelet transform analysis;

FIG. 15-1 is a schematic illustration of a curve of reflection peak saturation according to an embodiment of the present invention;

FIG. 15-2 is a schematic illustration of a plot of secondary reflections according to an embodiment of the present invention;

FIG. 15-3 is a schematic illustration of a plot of weld point gain according to an embodiment of the present invention;

15-4 are schematic diagrams of curves for special breakpoints according to embodiments of the present invention;

15-5 are schematic diagrams of curves of fractures according to embodiments of the present invention;

fig. 15-6 are schematic diagrams of unconnected curves of a pigtail according to an embodiment of the utility model.

Detailed Description

In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the utility model described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

Fig. 1 is a schematic view of an optical cable abnormality detection system according to an embodiment of the present invention, and as shown in fig. 1, according to an aspect of an embodiment of the present invention, there is provided an optical cable abnormality detection system including: an optical time domain reflectometer, a controller,

the optical time domain reflectometer is connected with the controller, and the output end of the optical time domain reflectometer is connected with one end of the monitored target optical cable and is used for transmitting a detection signal to the target optical cable and receiving a feedback signal of the target optical cable for reflecting the detection signal; the controller comprises a sampling module, a statistical module, a wavelet transform module and an analysis module; the sampling module is connected with the output end of the optical time domain reflectometer and is used for sampling the feedback signals according to a preset time interval to obtain feedback signals at a plurality of moments; the statistical module is connected with the sampling module and used for performing statistics on the feedback signals at a plurality of moments to generate corresponding optical power curves, and the wavelet transformation module is connected with the statistical module and used for performing wavelet transformation on the optical power curves to generate attenuation curves; the analysis module is connected with the wavelet transformation module and used for analyzing the attenuation curve through an analysis method and determining the position of the target optical cable where the abnormality occurs.

By the system, the optical time domain reflectometer and the controller are adopted, the optical time domain reflectometer is connected with the controller, and the output end of the optical time domain reflectometer is connected with one end of the target optical cable to be monitored, so that a detection signal is transmitted to the target optical cable, and a feedback signal of the target optical cable reflecting the detection signal is received; the controller comprises a sampling module, a statistical module, a wavelet transform module and an analysis module; the sampling module is connected with the output end of the optical time domain reflectometer and is used for sampling the feedback signals according to a preset time interval to obtain feedback signals at a plurality of moments; the statistical module is connected with the sampling module and used for performing statistics on the feedback signals at a plurality of moments to generate corresponding optical power curves, and the wavelet transformation module is connected with the statistical module and used for performing wavelet transformation on the optical power curves to generate attenuation curves; the analysis module is connected with the wavelet transformation module and used for analyzing the attenuation curve through an analysis method, determining the mode of the abnormal position of the target optical cable, performing wavelet transformation on the power curve according to the power curve of the feedback signal to obtain the attenuation curve, and determining the abnormal event and the position of the abnormal event according to the attenuation curve, so that the purpose of analyzing the attenuation curve obtained through the wavelet transformation of the feedback signal and effectively determining the abnormal event and the position of the abnormal event is achieved, the technical effect of improving the accuracy of optical cable abnormality detection is achieved, and the technical problem that optical cable fault detection in the related technology is not comprehensive and accurate enough is solved.

The detection signal can be a detection signal sent by an optical time domain reflectometer, the detection signal can be an optical signal with preset wavelength and pulse width, the optical time domain reflectometer sends the optical signal of the detection signal to a target optical cable, when the optical signal is transmitted along an optical fiber, the back scattering part of Rayleigh scattering at each position continuously returns to the incident end of the optical fiber, when the optical signal encounters a crack, Fresnel reflection can be generated, and the back reflection light can also return to the incident end of the optical fiber. The transmission characteristic, the length and the abnormal point of the optical fiber can be quantitatively measured by detecting the size and the arrival time of the back light at the input end through a photoelectric detector with proper optical coupling and high-speed response.

The feedback signal is a feedback optical signal generated by reflecting the optical signal of the detection signal by the target optical cable. The feedback signal may also be received by the optical time domain reflectometer and the optical power of the feedback signal determined.

The sampling module samples the feedback signals according to a preset time interval to obtain feedback signals at multiple moments, the power of the feedback signals at the multiple moments is determined according to a power calculation formula in the prior art, the first wavelength and the pulse width of the feedback signals at the multiple moments, the attribute parameters of a target optical cable and the second wavelength of a detection signal, and the power of the feedback signals at the multiple moments is counted by the counting module to generate a power curve. Therefore, feedback signals fed back by the detection signals are received, the power curve of the feedback signals is determined, and the related calculation processes are all the prior art.

Specifically, the power of the feedback signal at multiple moments is determined according to the first wavelength and the pulse width of the feedback signal at multiple moments, the attribute parameter of the target optical cable and the second wavelength of the detection signal. The method comprises the steps of receiving a feedback signal, and determining a first wavelength and a pulse width of the feedback signal; determining the power of the feedback signal according to the first wavelength and the pulse width of the feedback signal, the attribute parameter of the target optical cable and the second wavelength of the detection signal; wherein the power of the feedback signal is proportional to the pulse width of the feedback signal and the power of the feedback signal is inversely proportional to the second wavelength.

Given the parameters of the fiber, including the size of the light, attenuation coefficient, chromatic dispersion coefficient, mode field diameter, wavelength, bandwidth, and the like, the power of rayleigh scattering can be indicated, which is proportional to the pulse width of the signal if the wavelength is known: the longer the pulse width, the stronger the backscatter power. The power of rayleigh scattering is also related to the wavelength of the transmitted signal, with shorter wavelengths being more powerful.

The wavelet transformation module performs wavelet transformation on the power curve to obtain an attenuation curve, and the wavelet transformation module comprises the following steps: performing wavelet decomposition on the power curve to determine a wavelet coefficient; and reconstructing the power curve according to the wavelet coefficient to determine an attenuation curve.

Preferably, the second wavelength is 1550 nm. The 1310nm signal will produce a higher rayleigh backscatter than the 1550nm signal. In the high wavelength region (over 1500nm), rayleigh scattering continues to decrease, but another phenomenon called infrared attenuation (or absorption) occurs, increasing and leading to an increase in the overall attenuation value. Therefore, 1550nm is the lowest attenuation wavelength; this also explains why it is a wavelength for long distance communications. Naturally, these phenomena also affect the OTDR. As an OTDR at 1550nm wavelength, it also has low attenuation performance, and thus can be tested over a long distance.

Optionally, the optical time domain reflectometer includes a pulse generator, a coupler, and a photodetector, wherein the pulse generator is connected to an input/output terminal of the coupler, an output terminal of the coupler is connected to a section of the target optical cable to be monitored, and an end of the target optical cable connected to the coupler is further connected to the photodetector; the optical time domain reflectometer further comprises: and the driver is connected with the pulse generator and is used for driving the pulse generator to work.

Thereby driving the pulse generator to work and generating a detection signal. As shown in fig. 3, the pulse generator may be a light source module, and is composed of semiconductor lasers ECLD and DFB, a current driving source, and a temperature control source. The driver may be a driving control module, as shown in fig. 11, the driving control module is mainly responsible for generating a modulation signal or a driving signal of the laser, the acousto-optic modulator, and the polarization scrambler, and the driving module receives a system clock from the control module as a synchronization signal. The clock is distributed by the clock distributor and respectively output to the laser modulation circuit, the acousto-optic modulator modulation circuit and the scrambler driving circuit. The three sub-circuits comprise a laser modulation circuit, an acousto-optic modulator modulation circuit and a polarization scrambler driving circuit, work under the control of a synchronous clock, generate modulation or driving signals required by the modulation or driving circuits and output the modulation or driving signals respectively.

Optionally, the coupler includes a modulation device, an amplification device and a deflection disturbing device, an input end of the modulation device is connected to an output end of the pulse generator, an output end of the modulation device is connected to an input end of the amplification device, an output end of the amplification device is connected to an input end of the deflection disturbing device, and an output end of the deflection disturbing device is connected to the target optical cable; the modulation device and the deflection disturbing device are both connected with the driver.

The amplifying device may be a low noise amplifier LNA, as shown in fig. 5, and the polarization disturbing device may be a polarization disturbing module in fig. 5, and is composed of a polarization scrambler PS and a driving PS Driver thereof.

The control device is different from the controller, the control device is a component of the optical domain reflectometer, the control device can be the control module, as shown in fig. 13, the control module performs frequency multiplication on a clock signal of 100MHz generated by the crystal oscillator to obtain a system clock with higher frequency for the use of the FPGA core. This frequency multiplication is performed by a phase locked loop PLL. And the frequency-multiplied system clock enters a counter for counting, and the counting result is sent to a comparator. The comparator is composed of a series of timers, when the count value meets the trigger condition of a specific timer, corresponding signal jump is generated, and different timers correspond to different circuit modules. Through the process, the working sequence of each module can be accurately controlled. The phase-locked loop PLL is implemented by a phase-locked loop integrated inside the FPGA. The counter and the comparator are implemented by an FPGA. As shown in fig. 8, the digital frequency converter may be the digital down-conversion module in fig. 8.

Optionally, the wavelet transform module includes: the decomposition unit is connected with the statistical module and used for performing wavelet decomposition on the power curve to determine a wavelet coefficient; and the reconstruction unit is connected with the decomposition unit and used for reconstructing the power curve according to the wavelet coefficient through a reconstruction algorithm to determine the attenuation curve.

Performing wavelet decomposition on the power curve, wherein the determining wavelet coefficients comprises: decomposing the power curve according to the wavelet basis function and the decomposition layer number to obtain multilayer decomposition signals, wherein each layer of decomposition signals comprises a high-frequency part and a low-frequency part of a previous layer of signals; determining a high frequency coefficient of each layer of decomposed signal according to the high frequency part of each layer of decomposed signal; wavelet coefficients are determined based on high frequency coefficients of the multi-layered decomposition signal.

Specifically, the power curve can be reconstructed according to a reconstruction algorithm Mallat algorithm and a wavelet coefficient, and the attenuation curve is determined.

The analysis module is connected with the wavelet transformation module and used for analyzing the attenuation curve through an analysis method to determine the abnormal position of the target optical cable, wherein the analysis method is actually searching and comparing, and searching and comparing waveforms or parameters meeting the abnormal occurrence in the attenuation curve to determine whether the target optical cable is abnormal or not, and determining the abnormal position under the abnormal condition.

Specifically, the decomposition unit includes: the decomposition subunit is connected with the reconstruction unit and used for decomposing the power curve according to the wavelet basis function and the decomposition layer number to obtain a plurality of layers of decomposition signals, wherein each layer of decomposition signal comprises a high-frequency part and a low-frequency part of a previous layer of signal; the first determining subunit is connected with the decomposing subunit and used for determining the high-frequency coefficient of each layer of decomposed signal according to the high-frequency part of each layer of decomposed signal; and the second determining subunit is connected with the first determining subunit and used for determining the wavelet coefficients according to the high-frequency coefficients of the multilayer decomposition signals.

Optionally, the analysis module includes: the searching unit is connected with the reconstruction unit and used for searching and positioning the attenuation curve according to a preset amplitude threshold value; and the positioning unit is connected with the searching unit and used for determining the position of the target optical cable corresponding to the amplitude value and generating the abnormity of the reflection event under the condition that the amplitude value of the attenuation curve reaches a preset amplitude value threshold value.

The amplitude of the attenuation curve is judged through a preset amplitude threshold, the threshold can be determined through two steps, firstly, the threshold is roughly set, secondly, the threshold is further improved according to the preliminarily judged event interval, and then, the new threshold is used for positioning and fine position adjustment. Therefore, the accuracy can be improved, and the occurrence of misjudgment can be reduced.

Optionally, the analysis module further comprises: the preliminary positioning unit is connected with the reconstruction unit and used for searching the attenuation curve according to the waveness characteristics of the non-reflection event faults and determining a plurality of preliminary positioning points of the non-reflection event faults on the attenuation curve; the secondary positioning unit is connected with the primary positioning unit and used for determining the primary positioning point with attenuation reaching a preset attenuation threshold value as a normal starting point according to the attenuation of the plurality of primary positioning points; and the final positioning unit is connected with the re-positioning unit and used for determining the amplitude difference according to the curve amplitude of the position of the preset distance before and after the normal starting point, and determining the abnormity of the non-reflection event at the position of the target optical cable corresponding to the normal starting point under the condition that the amplitude difference reaches the preset difference value.

Specifically, the preliminary positioning point is determined, and a decision condition is set mainly according to the three characteristics of the curve at the non-reflection event, so as to find out a starting point which may meet the condition. The judgment condition should be properly relaxed, and there may be misjudgment but not missed judgment. Judging the attenuation of the starting point, removing abnormal events, and determining a normal starting point, wherein the simple operation is to calculate the y value difference of the starting point in the last step, namely the attenuation of the starting point, and if the y value difference is smaller than the required event attenuation threshold, the abnormal starting point is removed. The starting point position of the non-reflection event is accurately determined, and point-by-point judgment is carried out near the judged normal starting point by utilizing a more strict condition by utilizing the abrupt change characteristic of the starting point of the non-reflection event, so that the starting point position is more accurate.

A reflective event refers to an event where there is a reflection of light in the fiber, and a non-reflective event refers to an event where there is some loss in the fiber but no reflection of light, which produces a dip in the trajectory without an upward impact. Typically caused by fusion splicing, non-uniformity, aging, etc. of the optical fibers. The curve characteristic of the non-reflection event when the non-reflection event occurs, namely the judgment condition is as follows: the region before the event start point and the region after the event end point are both relatively flat, and the slope of the region between the event start points is large, and the attenuation is sharply reduced.

Optionally, the abnormality of the reflection event comprises at least one of: the peak value of the reflection peak is saturated; secondary reflection; negative loss; the anomaly of the non-reflection event includes at least one of: a special breakpoint; cracking the optical cable; and source end breakpoints.

The reflection peak value saturation is caused by the phenomenon that the peak value saturation occurs because the Fresnel reflection peak value is too large and the bandwidth of a receiver on hardware is limited;

secondary reflections, also known as ghosts, occur at the end of the fiber, caused by multiple reflections. The distance from the ghost position where the dotted line is to the previous reflection point is the same as the distance between the previous two reflection peaks;

the fusion point gain phenomenon, also called negative loss, is caused by fusion of optical fibers with different backscattering coefficients, and the optical fibers with large backscattering coefficients can be regarded as the dissolution loss in the reverse OTDR test;

the situation of special breakpoints is different from the situation that the common breakpoints cause larger reflection peaks, and the special breakpoints can cause the peak value of the reflection peak to be smaller or even almost not;

the crack occurs, the curve has obvious bulge but is different from the wave shape of the reflection peak, namely the point has medium mutation but does not form the end face condition, generally the crack position of the optical fiber;

when the tail fiber is not connected, the optical pulse cannot be transmitted, and the curve is abnormal, which is equivalent to that the breakpoint occurrence position is very close to the source end.

It should be noted that the present application also provides an alternative implementation, and the details of the implementation are described below.

Fig. 2 is a schematic diagram of a COTDR system architecture according to an embodiment of the present invention, and as shown in fig. 2, the research and design of an optical fiber fault early warning system are combined with an improved association rule mining algorithm, and the research is found through modeling and simulation, and the number of specific transaction records in a database can be greatly reduced through the improved association rule mining algorithm, and whether the item set is a frequent item set is determined according to the support degree of the item set, so that the search frequency and the time complexity of database data can be effectively reduced, and the early warning accuracy is high.

The physical framework of the COTDR system mainly comprises a light source module, a modulation module, an amplification module, a deflection disturbing module, a light receiving module, an analog-to-digital conversion module, a digital down-conversion module, a digital signal processing module, a control module, a driving control module and a power supply module. The light source module provides a continuous laser light source required by the COTDR system; one part of the light source module is connected with the light source modulation module, and the other part of the light source module is connected with the receiving module. The modulation module is used for pulse modulation of the continuous form light source module output, thereby generating the probe light pulse and the filling light complementary to the probe light pulse required by the system. The output of the modulation module is connected with the amplification module. The amplifying module is mainly used for amplifying the power of the FSK pulse generated by the modulating module to the design power required by the system. The amplifying module is connected with the deflection disturbing module. And the polarization disturbing module realizes that the polarization of the FSK pulse is uniformly and randomly distributed. It is connected to an external interface 1, the external interface 1 being an optical interface, and the interface 1 being connected to an external downstream optical cable. The balanced receiving module is connected to both the light source module and the external interface 2. The external interface 2 is an optical interface which is also connected to an external upstream cable. The receiving module detects weak Rayleigh scattering signals by using a coherent detection method and converts optical signals into electric signals. The analog-to-digital conversion module collects and quantizes the analog signals to obtain data corresponding to the analog signals. The analog-to-digital conversion module receives the intermediate frequency analog signal from the balanced receiving module, quantizes the intermediate frequency analog signal into a digital signal and transmits the digital signal to the subsequent digital down-conversion module.

The digital down-conversion module receives data of the intermediate frequency signal from the analog-to-digital conversion module, obtains data of the baseband signal through a down-conversion algorithm, and outputs the data to a subsequent digital signal processing module.

And the digital signal processing module receives the data of the baseband signal from the digital down-conversion module, performs FIR filtering and multipoint digital average BOXCAR, and analyzes the measurement result to obtain the running condition of the optical cable. The module communicates with an upper computer through an external interface 3 to transmit a measurement result. The interface is defined as a USB interface.

The control module is responsible for the operation of the synchronous analog-to-digital conversion module, the digital down-conversion module, the digital signal processing module and the driving module. The modules are connected through internal interfaces. The driving module generates driving signals of the light source module, the modulation module and the deflection disturbing module and is connected with the modules through an internal interface.

The analog signal is converted into data by the analog-to-digital conversion unit, and the signal corresponding to the data is the data of the intermediate frequency signal without down-conversion, is a data stream with 16 bits and 100MHz rate, and is transmitted to the digital down-conversion unit through a data channel. The digital down-conversion unit converts the intermediate frequency signal data through a data processing algorithm and extracts the data of the in-phase component and the orthogonal component of the baseband signal. Meanwhile, the speed of the data stream is reduced through data extraction. The output data of the digital down-conversion unit is the data of the in-phase component and the orthogonal component of the baseband signal, is two paths of data streams with 32 bits and the rate of about 10MHz, and is transmitted to the digital signal processing unit through a data channel. The digital signal processing unit performs digital filtering on the data of the in-phase component and the quadrature component of the baseband signal from the digital down-conversion unit to solve the data of the envelope of the baseband signal. The data is digitally averaged at multiple points to improve the signal-to-noise ratio. And analyzing the average result to obtain the operating condition of the optical cable. And the final average result and the analysis result are used as output data and are output to the data interface from the data channel. The data stream is a low speed data stream. The data interface is responsible for sending the data to the host computer.

The control unit is responsible for the generation and distribution of control signals. It generates a high-precision sampling clock signal, and outputs the sampling clock signal to the analog-to-digital conversion unit through the control channel. The data conversion unit performs analog-to-digital conversion in synchronization with the clock. The control unit generates synchronous and reset signals, and outputs the signals to the digital down-conversion unit, the digital signal processing unit and the driving unit through the control channel. The driving unit is responsible for generating modulation and driving signals of the acousto-optic modulator AOM, the laser and the polarization scrambler.

The most important interfaces among the logic function modules are data interfaces, which include a data bus Dbus, a 1-bit write clock signal line Rclk, and a 1-bit chip select signal line CS. The communication protocol mimics a FIFO write protocol to perform a write data operation on a unit that receives data when the communication initiating unit is to transmit the data.

Fig. 3 is a schematic view of a light source module according to an embodiment of the present invention, and as shown in fig. 3, the light source module is mainly composed of semiconductor lasers ECLD and DFB, a current driving source, and a temperature control source. The light source module provides a continuous laser source required by a COTDR system, wherein the ECLD is an external cavity semiconductor laser and is mainly characterized by narrow line width of output light and high wavelength stability. DFBs are semiconductor lasers commonly used for communications. In the design, the ECLD is an external cavity laser of EMCORE company, the specific model is ECCW-SMF-200-15-A-FA, the central wavelength of the ECLD is 1561.42nm, the output power is more than 15mW, and the line width is less than 10 KHz. The main reason for selecting the narrow linewidth ECLD as the detection light source is as follows: firstly, because the detection light source is used as a local oscillator for coherent detection, the coherent detection requires that the line width of the local oscillator light source is far smaller than the frequency bandwidth of a signal, the signal bandwidth in an online mode is 20KHz in design, and the signal bandwidth in an offline mode is 400KHz, so that the line width is selected to be about 10KHz, which is a commercial communication element with the narrowest line width that can be provided in the current market; secondly, due to the long single measurement time (120ms), the bandwidth of the following electrical filter is required to be smaller in order to obtain higher SNR in the design, so that the SNR can be improved by reducing the power of the band-pass noise. However, the small filter bandwidth limits the amount of wavelength drift of the local oscillator light source. The short term wavelength drift of a typical ECLD is about 120 KHz. Based on the above two conditions, we selected an ECLD with a line width of less than 10 HKz. The DFB is a semiconductor laser of JDSU company, which is a common LD in DWDM market at present. The main parameters of DFB we chose to use: the wavelength is 1562.23nm, the line width is less than 2MHz, and the maximum output power is 20 mW. Since DFB is used only as a fill light source, linewidth and stability are not very critical.

Good peripheral circuitry is important to ensure that a reliable LD output is obtained. Both ECLD and DFB are made with a 14-Pin butterfly package, and we have purchased the LD platform (model LDM4984), current source (LDX 3100), and temperature controller (LDT 5100) from ILXLIGHTWAVE as the drive modules for the LD. LDX3100 acts as a current source for the LD, with the main parameters being current up to 250mA, noise and ripple less than 2uA, short term stability less than 50ppm, and analog modulation input capability. LDT 5100 is used as an internal temperature controller and an external temperature controller of the LD, a bipolar floating point output type is adopted, the maximum output current is 2A, and the stability of temperature control can reach 5mK best. Since we do not know the temperature frequency shift coefficient of the ECLD, it cannot be estimated whether such temperature stability meets the system requirements. Since the drive of ILXLIGHTWAVE is a recommended product of ECLD, it can only be defaulted to meet the requirements, and an accurate determination must be given after the phase noise of the laser is measured. LDM4984 is the platform on which the 14-Pin butterfly LD is mounted, and the platform may be selectively temperature controlled. In this design, the ECLD uses secondary temperature control to ensure stable output of the laser, i.e., one LDT 5100 is used to control the temperature inside the ECLD, and the other LDT 5100 is used to control the temperature of the outer housing of the ECLD; the ECLD additionally uses a block LDX3100 to provide operating current thereto. The DFB laser uses a temperature controlled LDT 5100 to keep the temperature inside the laser stable, and uses a current source LDX3100 to supply the operating current. Since the linewidth of the laser of the DFB is only about 2MHz, and the stimulated brillouin scattering nonlinear effect is likely to occur, the linewidth of the laser is extended using PM in order to suppress brillouin scattering, and the driving of PM is derived from a noise signal of the control module.

Fig. 4 is a schematic diagram of a modulation module according to an embodiment of the present invention, and as shown in fig. 4, the main function of the modulation module is to generate FSK pulses with a high extinction ratio. AOM1 modulates probe light from the ECLD and AOM2 modulates fill light from the DFB. And Driver2 are the drive sources for AOM1 and AOM2, respectively. UK G & H company can provide acousto-optic products with high extinction ratio and steep rise time, so we chose its AOM product: the model of the AOM1 is M040-8J-F2S, and the model of the drive 1 is customized N21040-0.4 DMRE; AOM1 is model M18-2J-F2S, and its Driver2 is model A344A. The driving source is an RF source modulated by an external control signal and outputs a modulated RF pulse. The RF frequency distributions of Driver1 and Driver2 are 40MHz and 110 MHz. The custom Driver1 has the special function of outputting a continuous RF signal that can be used as a local oscillator to demodulate the bandpass signal generated by coherent detection, in addition to the RF pulses generated by the normal drive source. In the design, the control signals of Driver1 and Driver2 are mutually complementary electric pulses from the control module. Thus, under the action of the control signal, the AOM1 modulates the continuous probe light into probe light pulses with high extinction ratio >50dB and rise time of 110ns, and the central frequency of the probe light pulses generates 40MHz lower frequency shift; AOM2 modulates successive fill light pulses into complementary fill light pulses with high extinction ratio >50dB, rise time 25ns, and center frequency of the fill light pulses produces an up-shift of 110 MHz. While AOM1 is used herein to describe the generation of probe light pulses, in principle AOM2 can also be used to generate probe light pulses. If AOM2 is used to generate probe light pulses, a balanced probe with a wider frequency response bandwidth must be used; due to the adoption of the band-pass sampling technology, methods such as data acquisition and processing at the rear end can be kept unchanged. Through the composite action of WDM, the separated optical pulses multiplex FSK pulses with equal success rate. By means of the photodetector and the oscilloscope, strict equality of pulse power can be achieved by adjusting the driving current of the respective lasers. With the amplification of the EDFA we can amplify the FSK pulse to the appropriate power.

In addition, the FSK pulse has a gap of about 110ns, which is 1/50 of the pulse width relative to the pulse width of a longer detection pulse, such as 5us, and since the intensity of the generated rayleigh scattering signal is proportional to the pulse width, the effect of the gap on the rayleigh scattering intensity is only 1/50, and the design effect on the system performance is not great.

Fig. 5 is a schematic diagram of a polarization disturbing module according to an embodiment of the present invention, and as shown in fig. 5, the polarization disturbing module mainly comprises a polarization scrambler PS and a PS Driver for driving the polarization scrambler PS, and the PS Driver generates a driving current required by the PS. In the design, a 4-axis deflection disturbing module PCD-003 of general photonics is selected. The module is mainly characterized by an all-fiber structure, small insertion loss (<0.05dB) and high polarization disturbing frequency up to 700 KHz. The higher polarization disturbing speed can ensure that the polarization of the detection light in the pulse width time scale can be changed, so that the polarization fading effect can be better reduced. The polarization scrambling module mainly achieves randomizing the polarization of the FSK pulses, and the randomizing is uniformly distributed.

Fig. 6 is a schematic diagram of a balance detection module according to an embodiment of the present invention, as shown in fig. 6, which is composed of a 3dB Coupler, a BPD and a driver. The BPD is selected in the design instead of the common photoelectric detector, and the BPD can effectively eliminate residual noise caused by a local oscillator and effectively utilize the power of the local oscillator. Next, the BPD selected for use in the design was a product of Thorlabs, model number PDB 150C-EC-AC. The main criteria for selecting BPD are: detector wavelength range, detector dynamic range, saturation power, detector conversion gain and equivalent noise power. In addition to the offering of BPD by Thorlabs, New Focus offers similar products. We finally chose that the product of Thorlabs was primarily PDB150C capable of providing a 3dB bandwidth of 50MHz, which is exactly similar to the intermediate frequency (40MHz) generated by coherent detection. This provides relatively optimal conversion gain, and less noise power, due to the appropriate bandwidth. And PDB150C has a higher saturation power index of 5mW, and the dynamic range reaches 64dB at most. In addition, the PDB150C-EC-AC directly eliminates the influence of the DC signal by using an AC coupling mode. The BPDs provided by New Focus all use DC coupling. The local oscillator from the ECLD and the back rayleigh scattered signal from the external interface 2 are mixed at 3dB Coupler to produce the same two mixed lights and are input to the two ports of the BPD. The back Rayleigh scattering signal is formed in the optical cable by detecting the light pulse, and the back Rayleigh scattering signal carries information such as line loss, amplifier gain and the like, so that the health condition of the whole optical cable can be inferred by analyzing the intensity of the back Rayleigh scattering signal. Rayleigh scattering is essentially narrow-band Gaussian noise, and the envelope satisfies Rayleigh distribution. The center frequency of the probe optical pulse is shifted by 40MHz with respect to the local oscillator due to the modulation by the AOM. So after coherent detection, the voltage output from the BPD contains a signal and strong background noise.

Fig. 7 is a schematic diagram of an analog-to-digital conversion module according to an embodiment of the present invention, and as shown in fig. 7, a module in the circuit responsible for converting an intermediate frequency analog signal into data is an analog-to-digital conversion module. The low voltage signal from the photoelectric detector is amplified by the low noise amplifier LNA, the voltage amplitude is improved, and the low voltage signal is filtered by the band-pass filter to filter noise components. The filtered analog signal enters an analog-to-digital converter (ADC), is converted into data and is output to a subsequent digital down-conversion module.

The intermediate frequency signal first enters a low noise amplifier LNA for amplification. The intermediate frequency signal from the photodetector has a voltage amplitude below 1mV, and most ADCs have an input voltage rangeAround 1V or more, this requires the use of an LNA to amplify the if signal. There are three main requirements for LNA performance: sufficient gain, suitable bandwidth, and as low noise as possible. An AD603 programmable gain amplifier of AD company is selected to form the LNA. The gain of the amplifier is-10 dB-30 dB at 90MHz bandwidth, and the noise spectrum density is 1.3nV/(Hz)^0.5The use of the LNA can be cascaded, and two LNAs with 30dB gain are used in series, so that an LNA with 60dB gain is obtained. The output signal of the LNA enters an analog band-pass filter BP for filtering. The BP has two functions, one is to filter noise frequency components on a frequency band outside a pass band; and the other is to perform anti-aliasing filtering for the analog-to-digital conversion of the rear end. This can be achieved using an RLC filter, considering that further filtering can be done in the digital domain, the primary task of BP is also to prevent aliasing. The performance requirements of the analog filter are related to the characteristics of the sampling rate. If the out-of-band noise power spectral density is 30dB stronger than the signal power density spectrum, a band-pass filter with a stop-band attenuation characteristic higher than 70dB is necessary to ensure that the signal-to-noise ratio after ADC quantization is more than 40 dB. The lower the sampling rate, the closer the stopband frequency of the analog filter is required to the passband frequency. In contrast, the filter design difficulty rises. For a sampling rate of 100MHz, a butterworth filter of order 4 may suffice. The analog-to-digital conversion chip ADC is responsible for collecting and quantizing analog signals into data. The most important indexes of the ADC chip are quantization bit number and sampling rate. These two metrics directly determine the physical resolution of the receiver. To fully utilize the existing mature technology, we chose the ADC chip AD9446 from Analog Devices. The high-speed high-precision analog-to-digital converter has the quantization precision reaching 16 bits and the highest sampling rate reaching 100 MSPS.

FIG. 8 is a schematic diagram of a digital down converter module according to an embodiment of the present invention, as shown in FIG. 8, the output data of the analog-to-digital conversion module enters the digital down converter at a rate of 1.6 Gbit/s. The NCO of the numerical control oscillator generates strictly orthogonal digital local oscillators, digital frequency mixing is carried out on the digital local oscillators and input data respectively, low-pass filtering is carried out on the frequency mixing result through a Comb Integration (CIC) filter, high-frequency components are filtered, and in-phase components and orthogonal components of baseband signals are obtained. The two data extractors respectively extract the in-phase component and the orthogonal component by a factor D, and the data rate is reduced to (1.6/D) Gbit/s. And the extracted data is used as an output signal of the digital down-conversion module and is transmitted to a subsequent data processing module. The data stream is a 16bit by 100MHz data stream between the ADC and the digital down converter. And a 16-bit parallel data line is adopted to connect the ADC and the digital down-conversion unit. The physical interconnection mode is a microstrip line on a PCB (printed Circuit Board), the characteristic impedance is defined to be 110 ohms, and serial impedance matching is adopted at an ADC (analog to digital converter) end. The data flow enters a digital down converter for processing, and is reduced to a low-speed data flow of 32bit multiplied by 5MHz through data extraction. In the case of 12000Km, the required data storage space is ((2x12000/2x105) x32 × 5x106) ═ 18 Mbit. The number of bits of data can be relaxed appropriately, taking 36Mbit into account the finite word length effect. This can be achieved by extending SRAM or SDRAM outside the FPGA.

The digital down conversion module is realized in the FPGA. The module is an adder except for two embedded multipliers required by a digital mixer in hardware. The comb-integration (CIC) filter is similar in structure to the IIR filter but has coefficients of 1 and-1, so that no multiplication is required. The NCO is a local oscillator implemented in the digital domain, which is essentially a discrete sine wave amplitude value. Quadrature outputs are guaranteed by using quadrature phases to calculate sinusoidal amplitude values, the resulting error being determined only by the word length of the data representing the amplitude.

And averaging and outputting the filtering result of the CIC according to every D data points, thereby completing the conversion from the high-speed data stream to the low-speed data stream. The averaging and data extraction processes may be performed using only adders.

For the digital down-conversion module, the hardware structure is simple, and the requirement on the scale of logic resources is not high, so that the digital down-conversion module can be realized by using a small-scale high-speed FPGA device. The specific computation estimation and simulation of the part are shown in appendix 10.6. The specific indexes thereof include: more than two 16 x 16 embedded multipliers are provided, and the core operating frequency is more than 200 MHz. The clone II series FPGA from Altera corporation can meet this requirement.

Fig. 9 is a schematic diagram of a digital signal processing module according to an embodiment of the present invention, and as shown in fig. 9, output data of the digital down-conversion module is divided into an in-phase component and a quadrature component and enters the digital signal processing module. The in-phase and quadrature components of the baseband signal from the digital down-conversion module are respectively fed into the FIR filter for further filtering to reduce the interference of the noise component. The result of the filtering is summed by squaring, yielding data of the envelope characteristic of the baseband signal. The enveloped data enters a multipoint digital averager BOXCAR for averaging, and the signal-to-noise ratio is improved. And the average final result is analyzed by the DSP to obtain the running condition of the optical cable. The FIR filter used in this block is still a low-pass filter, but the out-of-band attenuation characteristic is required to be steeper to eliminate the influence of the out-of-band noise on the measurement as much as possible.

Fig. 10 is a schematic diagram of a 5-tap FIR filter according to an embodiment of the present invention, and as shown in fig. 10, a typical 5-tap FIR filter is implemented by a series of multipliers, adders and shift registers mainly in hardware. For the application of this module, a FIR filter of more than 100 orders is necessary, which means that this module requires more FPGA logic resources in terms of hardware implementation. But because the data flow of the module is the low-speed data flow which is extracted, the requirement on the working speed of the FPGA is low. The quantization noise in the FPGA is determined by the word length of the representation data, and high-precision data can be used in the calculation, for example, FIR filtering can be performed on 16-bit data, a tap coefficient of the FIR filter can be selected to be 17 bits, so that the high 32 bits of the product can ensure the precision, and the final calculation result is subjected to tail-clipping processing as required. Since the useful component of the original signal is buried in extremely white noise, the useful signal must be recovered by a specific method. The most common method is multipoint digital averaging (BOXCAR).

And during the (N + 1) th measurement, the FPGA takes out the sum of the results of the previous (N) th measurements and adds the sum to the new data of the (N + 1) th measurement, and meanwhile, the divider reads the value in the RAM in parallel and divides the value to obtain the average value of the previous (N) th data to be output. The sum of the data of the first N +1 times is stored as new data in the data memory RAM. The BOXCAR technique utilizes the correlation of periodic signals, and thus the difficulty in achieving BOXCAR is periodic synchronization rather than a specific operation structure. From the properties of BOXCAR, it is known that more data points are available for averaging to be more beneficial to recover the signal, and thus it is beneficial to increase the sampling rate. In hardware architecture, the body of BOXCAR is a sequentially accessible data memory RAM and an adder. The divider can be implemented with a shift register by choosing to average the powers of 2. The DSP is mainly used for analyzing data, extracting working points with possible faults, and is responsible for communication with an upper computer and assisting operation of a management system. Because the functions are completed by using software programming, the functions are more flexible, and stronger upgrading margin is provided. The main operations of the DSP include spectral analysis, filtering, and fault identification.

Fig. 11 is a schematic diagram of a driving control module according to an embodiment of the utility model, and as shown in fig. 11, the driving control module is mainly responsible for generating modulation signals of the laser, the acousto-optic modulator, and the polarization scrambler, in other words, the driving circuits of the three circuits are sequentially operated under the control of the driving control module. Since the driving control circuit is a module independent of the driving of each circuit, and the working time sequence of each driving circuit has a strict precedence order, we will make a section of the driving control module separately, and discuss it specifically. The driving control module is mainly responsible for generating modulation signals or driving signals of the laser, the acousto-optic modulator and the polarization scrambler, and the driving module receives a system clock from the control module as a synchronous signal. The clock is distributed by the clock distributor and respectively output to the laser modulation circuit, the acousto-optic modulator modulation circuit and the scrambler driving circuit. The three sub-circuits work under the control of a synchronous clock to generate modulation or driving signals required by the sub-circuits respectively and output the modulation or driving signals respectively. Fig. 12-1 is a schematic diagram of a laser modulation circuit according to an embodiment of the present invention, a block diagram of which is shown in fig. 12-1.

In order to tune the center frequency of the laser to a normal distribution, a white noise-like modulated current signal needs to be added to the laser. The modulation signal is generated by a laser modulation circuit. The pseudo-random sequence generator generates a pseudo-random sequence under the control of the synchronous clock, and the distribution of the sequence values is approximately white noise distribution. The pseudo-random sequence enters a digital-to-analog converter (DAC) to complete the conversion from a digital signal to an analog signal. The analog signal is in the form of a voltage and cannot directly modulate the laser. And inputting the analog voltage signal into a voltage-controlled current source to perform transconductance conversion to obtain a final modulation current signal. In a specific hardware implementation, the pseudo-random sequence generator is composed of a 16-bit shift register and a series of modular two-adder taps, which can be implemented by using an FPGA, and the consumed logic resource is small. The acousto-optic modulator needs the action of a modulation signal to generate the detection light pulse. FIG. 12-2 is a schematic diagram of an acousto-optic modulator modulation circuit, a block diagram of an acousto-optic modulator modulation circuit, according to an embodiment of the utility model, as shown in FIG. 12-2.

The counter receives the synchronous clock for counting, and the counting result is output to the pulse generator. The pulse generator generates a pulse signal of a specific period and duty ratio according to the output of the counter. The pulse signal is divided into two paths, wherein one path is inverted through an inverter to obtain a signal complementary with the original pulse, and the two paths of signals enter a power amplifier for amplification to obtain a modulation signal required by the modulation acousto-optic modulator. On a specific hardware implementation, the main body of the circuit is a counter and a comparator, which can be implemented by using an FPGA, and consumed logic resources are small. Fig. 12-3 is a schematic diagram of a polarization scrambler driving circuit according to an embodiment of the present invention, and a block diagram of the polarization scrambler driving circuit is shown in fig. 12-3. From the composition of the circuit, the circuit is mainly divided into three parts: signal generation, amplitude discrimination feedback and phase discrimination feedback.

Fig. 13 is a schematic diagram of a control module according to an embodiment of the present invention, and as shown in fig. 13, the control module is responsible for generating and distributing a system clock and synchronizing operations of various modules in the system. The control module performs frequency multiplication on a 100MHz clock signal generated by the crystal oscillator to obtain a system clock with higher frequency for the FPGA core to use. This frequency multiplication is performed by a phase locked loop PLL. And the frequency-multiplied system clock enters a counter for counting, and the counting result is sent to a comparator. The comparator is composed of a series of timers, when the count value meets the trigger condition of a specific timer, corresponding signal jump is generated, and different timers correspond to different circuit modules. Through the process, the working sequence of each module can be accurately controlled. The phase-locked loop PLL is implemented by a phase-locked loop integrated inside the FPGA. The counter and the comparator are implemented by an FPGA. Likewise, the consumed logic resources are small and may be disregarded relative to the consumption of the digital down conversion module and the digital signal processor module.

The OTDR curve event feature identification positioning algorithm of this embodiment: the OTDR test data file returned from the monitoring station is actually made up of many data points. After the OTDR sends a certain pulse of test light, it receives the optical signal scattered back through the optical fiber transmission, because the distance of the optical fiber can be indirectly characterized by the time of the optical signal transmission, the OTDR samples the scattered back optical signal according to a certain time interval, and the logarithmic value of the ratio of the optical power value obtained by sampling to the initial optical power value sent by the OTDR is the relative optical power value of the sampling point. And taking the relative backscattering power dB value of the sampling point as a vertical coordinate, and taking the position of the sampling point on the measured optical fiber calculated according to the propagation time of the sampling point as a horizontal coordinate (km), so as to obtain the OTDR test curve.

The purpose of analyzing the OTDR curve is to find out whether there are any events such as fiber breakage, splice, bending, etc. from the curve, so that it is the basis of curve analysis to know the characteristics of the OTDR curve and the characteristics of the events represented on the curve. Generally, events on the OTDR test curve can be classified into the following.

(1) Blind areas: the measurement of the fiber had a blind spot at the beginning, which was caused by the strong fresnel reflection at the beginning of the fiber.

(2) Normal attenuation region of the optical fiber: in the process of light traveling, due to factors such as impurities and bubbles in the optical fiber, transmission energy of the light is lost as scattering, and due to the Rayleigh scattering effect, the power of a back scattering signal transmitted back from the optical fiber is attenuated according to the rule of the normal attenuation coefficient of the optical fiber to form a region, and the ordinate of the curve is the value of optical power db, so that the region is represented as a straight line which uniformly descends according to a certain slope.

(3) Non-reflective events: when an optical fiber has a fusion splice or is bent, the attenuation of the optical fiber rapidly decreases, and a relatively large attenuation occurs at the position of the occurrence of the event.

(4) Reflection events: at the position of the optical fiber loose joint or the optical fiber breakage, a relatively large reflection peak is formed due to relatively large Fresnel reflection, and meanwhile, relatively large attenuation is also realized.

(5) Fiber end: larger Fresnel reflection also occurs at the end of the fiber, so there is also a higher reflected pulse, and at the same time, since the fiber has reached the end, the noise interference is larger, so there is finally a section of noise jitter area. From the above description, it can be seen that the basic form of the OTDR backscattering curve is a uniform descending slope, and events with more distinct characteristics appear in the middle, and the purpose of curve analysis is achieved as long as we find the events in the uniform slope.

OTDR event location conventional algorithm: the mutation points on the data curve returned by the optical fiber test carry rich information which can be used for pattern recognition, and various methods for performing event positioning analysis on the OTDR curve are provided, and compared with the traditional method, the two-point method and the least square method are combined for use. But its accuracy is low.

Fig. 14-1 is a schematic diagram of an OTDR test curve according to an embodiment of the present invention, and fig. 14-2 is a schematic diagram of a curve after Gabor transform analysis is performed on the test curve of fig. 14-1. As shown in fig. 14-1 and 14-2, the OTDR curves used and the analysis results using Gabor transform. The selection of the OTDR trace with higher noise level of fig. 14-1 and fig. 14-2 well illustrates that Gabor transform is used for event positioning, and compared with the two-point method, the detection accuracy is obviously improved. The Gabor transform results are almost all zeros at non-event point locations, while the values at event points are large, clearly locating the a1-a5 event points.

However, as can be seen from the details of the Gabor transform result, since the specific waveform has an oscillatory nature, the detection needs to search by the width of the window function to skip the invalid oscillation point. Although this method can improve the positioning error, its oscillation will bring the difficulty of selecting the decision threshold.

In addition, under different event resolutions, the number of points calculated by Gabor conversion is different, so that certain pressure is brought to the selection of the judgment threshold. Although the Gabor transform overcomes the defects of the conventional fourier transform, can realize the time domain local characteristic analysis of signals, has better performance in the OTDR event positioning, and still has a plurality of defects. Firstly, the local analysis capability of the Gabor transform signal is limited, and since the time domain width and the frequency domain width of the window function satisfy the uncertainty principle, the time domain resolution and the frequency domain resolution may not be optimal at the same time. The smaller the time width is, the higher the time domain resolution is, and the worse the frequency domain resolution is, in the actual OTDR curve data analysis, it is desirable to automatically adjust the size of the time width according to different measurement results, and the Gabor method cannot satisfy this adaptivity.

An event point detection algorithm based on wavelet transformation comprises the following steps: the principles of wavelet decomposition have been elaborated in the foregoing, and are not described further herein. In which the authors used the bior3.5 wavelet to analyze the OTDR raw signal, with the following results:

fig. 14-3 is a schematic diagram of the test curve of fig. 14-1 after analysis of the wavelet transform, and as shown in fig. 14-3, events a1-a5 can also be accurately located in OTDR trace data with higher noise level using wavelet transform, with coefficients near zero from the noise portion at non-event points. And different from Gabor transform, details in fig. 14-3 show that the wavelet transform has better spectrum concentration, shows the wavelet characteristic and has stronger discrimination operability.

Therefore, although the wavelet transform has the capability of adaptive time-frequency analysis, the selection of the scale of the wavelet transform is still an important factor which is difficult to balance in event positioning. If the scale is smaller, the peak value of the corresponding position of the event point coefficient is small, and the influence of the wavelet coefficient of the noise is larger, so that errors are easily caused in the judgment of subsequent event points. As the scale increases, the number of coefficient points describing the event increases. Meanwhile, the wavelet coefficient of the noise is well suppressed, and as can be seen from the details in fig. 14-3, the peak value of the effective coefficient representing the event information also becomes higher correspondingly, which is beneficial to the event discrimination.

Algorithm comparison and analysis:

considering the robustness of the algorithm, the most critical factor influencing the positioning results of the two-point method and the least square method is the noise threshold. As the noise level increases, the performance of the algorithm degrades significantly. For GT and WT, the algorithm robustness of the former is determined by the window function width and the number of Gabor coefficient calculation points, and the latter is determined by the wavelet function type and the wavelet analysis scale, and both are influenced by the discrimination threshold. The window function width directly determines the event resolution of the GT, and the number of points of the Gabor coefficient represents the accuracy of describing the event.

In view of the complexity of the algorithm, the algorithm combining the two-point method and the least square method is easiest to implement. The wavelet transform method is the most complex, and the complexity of the algorithm of the Gabor transform is between the two. Therefore, in the early OTDR curve event positioning algorithm, due to the limitation of the computer and the backward velocity, a simple algorithm combining a two-point method and a least square method is mostly adopted. But this method is less tolerant to noise and thus has poor detection and localization performance. Compared with the wavelet transform method, although the calculation is complex and the programming is difficult to realize, the wavelet transform method has self-adaptive time-frequency analysis capability and better detection performance. The Gabor transform method can be regarded as a compromise between the two methods.

In recent years, with the continuous improvement of computer performance, the recognition algorithm of wavelet analysis is gradually becoming the mainstream algorithm of OTDR event detection because of its excellent positioning capability. Researchers have conducted many studies on the OTDR event locating algorithm of wavelet domain analysis. In 2003, populus and china, etc. of the university of the beijing industry, utilized the modulus maximum of wavelet transformation to detect the singular point of the OTDR signal curve, realized the location of the event point, and had better accuracy. In 2005, duchenhui et al, university of vinpoch science, used haar wavelet decomposition to analyze the OTDR signal curve to locate the fiber fault point. In 2011, the strangeness analysis is performed on the OTDR curve by utilizing the localized features of the wavelet transform space, so that the event positioning of the OTDR curve is realized, and a better effect is obtained in the test. In 2015, the hole balance and the like provide an improved event positioning algorithm, and an algorithm combining short-time Fourier transform and model matching improves the accuracy and efficiency of event positioning of the algorithm. In 2016, methods for positioning fiber reflection events and non-reflection events in a wavelet domain are designed by Brilliant wave et al. The design method is already applied to actual engineering. There are also many researchers studying event localization algorithms, and recent localization algorithms are mainly based on wavelet transform.

OTDR curve event feature identification algorithm: the identification of specific events of the OTDR curve is very important work, the identification of events of the OTDR curve is mainly carried out by experienced workers at the present stage, and related algorithm research is less. This creates a lot of difficulties in the maintenance of the optical fiber, so it is of great importance to develop an effective event recognition algorithm for the OTDR curve of the optical fiber. In actual testing, many complications arise due to the hardware and network environment, the different effects of the measurement environment, and the complexity of fiber failures.

(a) FIG. 15-1 is a diagram illustrating a reflection peak saturation curve according to an embodiment of the present invention, as shown in FIG. 15-1, because the peak value of the Fresnel reflection peak is too large, the receiver bandwidth is limited in hardware, and the peak saturation phenomenon occurs;

(b) FIG. 15-2 is a schematic diagram of a curve of a secondary reflection according to an embodiment of the present invention, as shown in FIG. 15-2. FIG. 15-2 is a diagram of a situation where a secondary reflection, also known as ghost, occurs, typically at the end of an optical fiber, due to multiple reflections. The distance from the ghost position where the dotted line is to the previous reflection point is the same as the distance between the previous two reflection peaks;

(c) FIG. 15-3 is a schematic diagram of a plot of splice point gain according to an embodiment of the present invention, as shown in FIG. 15-3, FIG. 15-3 is a graph of the splice point gain phenomenon, also known as negative loss, caused by the fusion of fibers having different backscattering, after which the fiber having a large backscattering coefficient can be considered as the dissolution loss in an inverse OTDR test;

(d) fig. 15-4 is a schematic diagram of a curve of a special breakpoint according to an embodiment of the present invention, as shown in fig. 15-4, fig. 15-4 is a diagram of a situation where a special breakpoint occurs, and unlike a general breakpoint causing a large reflection peak, the special breakpoint may cause a small or even almost no reflection peak value;

(e) FIG. 15-5 is a schematic view of a crack curve according to an embodiment of the present invention, as shown in FIG. 15-5, FIG. 5-5 shows a crack condition, where the curve is significantly convex, but is different from the reflection peak waveform, i.e., where the point has a medium abrupt change but does not form an end face condition, typically a fiber crack location;

(f) fig. 15-6 are schematic diagrams of unconnected curves of the pigtails according to the embodiment of the present invention, as shown in fig. 15-6, fig. 5-6 show that when the pigtails are unconnected, the optical pulse cannot be transmitted, and the curves are abnormal, which is equivalent to that the position of the breakpoint is very close to the source end.

Only a few abnormal fault conditions are listed here, and in fact more complex conditions occur, which puts high requirements on the design of the algorithm. Since reflection events and non-reflection events on a fiber OTDR curve have significantly different characteristics, researchers typically consider the identification of reflection events and non-reflection events separately and design different algorithms. The identification algorithms for common reflection events and non-reflection events will be described separately below.

Identification of reflection events: the reflection events are distinguished and positioned by wavelet analysis, the waveforms of the reflection events show that local mutation can occur on an attenuation curve, and the wavelets have elasticity, so that the wavelet analysis method is very suitable for analyzing local characteristics of the curve when the scale is reduced. Thus, when wavelet decomposition is carried out on the signal, the large-amplitude reflection impact position is necessarily corresponding to a large wavelet coefficient value, and the reflection event can be judged based on the simple threshold judgment method.

The specific steps of judging the result are as follows:

(1) the signal is wavelet decomposed (chosen as wavelet basis since the 'dbl' wavelet shape is very similar to the impulse).

(2) And reconstructing the signal by using the high-frequency coefficient of the first-order decomposition. This substantially removes the effects of rayleigh back reflections with little effect on abrupt portions of high frequencies.

(3) Setting a threshold value for positioning the event. In engineering practice, it is found that in order to eliminate noise influence, a threshold value can be determined through two steps, the threshold value is roughly set, then the threshold value is further improved according to an event interval which is preliminarily judged, and then the new threshold value is used for positioning and fine position adjustment. Therefore, the accuracy can be improved, and the occurrence of misjudgment can be reduced.

The event model is selected by the following steps: firstly, ensuring that a reflection peak with a normal pulse shape in the test is selected as an analysis model; secondly, the number of the selected model points is ensured to be appropriate as much as possible, namely the initial point of the reflection peak is taken to the position of the attenuation blind area. Based on the two principles, the RMT (reflective matching models) can be closer to the actual and real pulse shape, so that a foundation is laid for correlation matching, and the accuracy of event positioning is improved. After the event model is selected, the normalized correlation coefficients of the specified part of the curve and different models are calculated to match, so that the event identification is carried out.

Identification of non-reflection events: non-reflective events are events in which there is some loss in the fiber but no reflection of light, which produces a dip in the trajectory without an upward impact. Typically caused by fusion splicing, non-uniformity, aging, etc. of the optical fibers. The curve characteristic of the non-reflection event when occurring is as follows: the region before the event start point and the region after the event end point are both relatively flat, and the slope of the region between the event start points is large, and the attenuation is sharply reduced. Therefore, it is necessary to perform slope analysis on the corresponding sample segment point by point, and detect the non-reflection event according to whether the slope meets the above characteristic change.

This embodiment exemplifies an improved threshold decision method for detecting non-reflected events in an OTDR curve. The method comprises the following steps:

(1) initially positioning a starting point;

the method mainly sets a judgment condition according to the three characteristics of the curve at the non-reflection event, and finds out a starting point which possibly meets the condition. The judgment condition should be properly relaxed, and there may be misjudgment (but not much), but not missed judgment.

(2) Judging the attenuation of the starting point and removing abnormal events;

the simple operation is to calculate the y value difference (approximate to the starting point decay) of the starting point in the last step, and if the y value difference is smaller than the required event decay threshold, the event is removed.

(3) Accurately determining the position of a starting point;

and the abrupt change characteristic of the starting point is utilized, and the point-by-point judgment is carried out near the judged starting point by utilizing a stricter condition, so that the position of the starting point is more accurate. Non-reflective minor events are effectively detected.

Existing algorithms generally only recognize whether an event is a reflection event or a non-reflection event, and there is no good means of discriminating between specific cases of events. The existing methods are various, such as a simple threshold detection method, a correlation matching method, a Gabor transform domain analysis method, a wavelet domain analysis method and the like, but the effects are not ideal. The correlation matching algorithm is the one with relatively good effect, and has the capability of identifying different event types. It is contemplated that an event library may be created and the identification of the event type may be made by verifying the matching of the pattern at the OTDR event to the patterns in the event library. It is further noted that the event recognition problem of OTDR curves is a typical graph classification problem, and the method using machine learning may be very suitable, which may be the future development direction.

The above-mentioned serial numbers of the embodiments of the present invention are merely for description and do not represent the merits of the embodiments.

In the above embodiments of the present invention, the descriptions of the respective embodiments have respective emphasis, and for parts that are not described in detail in a certain embodiment, reference may be made to related descriptions of other embodiments.

In the embodiments provided in the present application, it should be understood that the disclosed technology can be implemented in other ways. The above-described embodiments of the apparatus are merely illustrative, and for example, the division of the units may be a logical division, and in actual implementation, there may be another division, for example, multiple units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, units or modules, and may be in an electrical or other form.

The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.

In addition, functional units in the embodiments of the present invention may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit. The integrated unit can be realized in a form of hardware, and can also be realized in a form of a software functional unit.

The integrated unit, if implemented in the form of a software functional unit and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present invention may be embodied in the form of a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present invention. And the aforementioned storage medium includes: a U-disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a removable hard disk, a magnetic or optical disk, and other various media capable of storing program codes.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims

1. An optical cable anomaly detection system, comprising: an optical time domain reflectometer, a controller,

the optical time domain reflectometer is connected with the controller, and the output end of the optical time domain reflectometer is connected with one end of a monitored target optical cable and is used for transmitting a detection signal to the target optical cable and receiving a feedback signal of the target optical cable reflecting the detection signal;

the controller comprises a sampling module, a statistical module, a wavelet transformation module and an analysis module;

the sampling module is connected with the output end of the optical time domain reflectometer and is used for sampling the feedback signals according to a preset time interval to obtain feedback signals at multiple moments; the statistical module is connected with the sampling module and used for performing statistics on the feedback signals at multiple moments to generate corresponding optical power curves, and the wavelet transformation module is connected with the statistical module and used for performing wavelet transformation on the optical power curves to generate attenuation curves; and the analysis module is connected with the wavelet transformation module and used for analyzing the attenuation curve through an analysis method and determining the position of the target optical cable with abnormality.

2. The system of claim 1, wherein the wavelength of the detection signal output by the output of the optical time domain reflectometer is greater than a wavelength threshold, wherein the wavelength threshold is 1300nm to 1700 nm.

3. The system of claim 1, wherein the optical time domain reflectometer comprises a pulse generator, a coupler, and a photodetector, wherein the pulse generator is connected to an input/output terminal of the coupler, an output terminal of the coupler is connected to a section of the target cable to be monitored, and an end of the target cable connected to the coupler is also connected to the photodetector;

the optical time domain reflectometer further comprises: and the driver is connected with the pulse generator and is used for driving the pulse generator to work.

4. The system of claim 3, wherein the coupler comprises a modulating means, an amplifying means, and a polarizing means,

the input end of the modulation device is connected with the output end of the pulse generator, the output end of the modulation device is connected with the input end of the amplification device, the output end of the amplification device is connected with the input end of the deflection disturbing device, and the output end of the deflection disturbing device is connected with the target optical cable;

the modulation device and the deflection disturbing device are both connected with the driver.

5. The system of claim 4, wherein the optical time domain reflectometer further comprises: the control device, the signal processing device and the output interface;

the control device is connected with the input end of the driver;

the signal processing device comprises a digital-to-analog converter, a digital frequency converter and a digital signal processor;

the input end of the digital-to-analog converter is connected with the control device and the output end of the receiver, and the input end of the receiver is connected with the target optical cable; the output end of the digital-to-analog converter is connected with the input end of the digital frequency converter, the input end of the digital signal processor is connected with the output end of the digital frequency converter, and the digital signal processor is connected with the output interface.

6. The system of claim 1, wherein the wavelet transform module comprises:

the decomposition unit is connected with the statistic module and used for performing wavelet decomposition on the power curve to determine a wavelet coefficient;

and the reconstruction unit is connected with the decomposition unit and used for reconstructing the power curve according to the wavelet coefficient through a reconstruction algorithm to determine the attenuation curve.

7. The system of claim 6, wherein the decomposition unit comprises:

the decomposition subunit is connected with the reconstruction unit and used for decomposing the power curve according to the wavelet basis function and the decomposition layer number to obtain multilayer decomposition signals, wherein each layer of decomposition signals comprises a high-frequency part and a low-frequency part of a previous layer of signals;

the first determining subunit is connected with the decomposing subunit and used for determining the high-frequency coefficient of each layer of decomposed signal according to the high-frequency part of each layer of decomposed signal;

and the second determining subunit is connected with the first determining subunit and used for determining the wavelet coefficients according to the high-frequency coefficients of the multilayer decomposition signals.

8. The system of claim 6, wherein the analysis module comprises:

the searching unit is connected with the reconstruction unit and used for searching and positioning the attenuation curve according to a preset amplitude threshold value;

and the positioning unit is connected with the searching unit and used for determining the position of the target optical cable corresponding to the amplitude value under the condition that the amplitude value of the attenuation curve reaches the preset amplitude value threshold value, and the abnormal condition of the reflection event occurs.

9. The system of claim 8, wherein the analysis module further comprises:

the preliminary positioning unit is connected with the reconstruction unit and used for searching the attenuation curve according to the waveness characteristics of the non-reflection event faults and determining a plurality of preliminary positioning points of the non-reflection event faults on the attenuation curve;

the secondary positioning unit is connected with the primary positioning unit and used for determining the primary positioning point with attenuation reaching a preset attenuation threshold value as a normal starting point according to the attenuation of the plurality of primary positioning points;

and the final positioning unit is connected with the re-positioning unit and used for determining an amplitude difference according to the curve amplitude of the position of the preset distance before and after the normal starting point, and determining that the position of the target optical cable corresponding to the normal starting point is abnormal in a non-reflection event under the condition that the amplitude difference reaches a preset difference value.

10. The system of claim 9, wherein the anomaly of the reflection event comprises at least one of:

the peak value of the reflection peak is saturated; secondary reflection; negative loss;

the anomaly of the non-reflection event includes at least one of:

a special breakpoint; cracking the optical cable; and source end breakpoints.