CN111211832B - A method and system for determining the operating state of an optical cable based on polarization mode dispersion - Google Patents

Abstract

The invention discloses a method and a system for determining the running state of an optical cable based on polarization mode dispersion. The real-time PMD value is compared with the preset PMD value and the matching quantitative relationship table, and the matching quantitative index of the optical cable to be measured is determined; according to the real-time PMD value of the optical cable to be measured and the The matching quantification index is used to match the force type based on the preset time spectrum of the force type, and determine the force type of the external force received by the optical cable to be tested. In the method for determining the operating state of an optical cable based on polarization mode dispersion of the present invention, after the real-time PMD value of the cable to be tested is determined, it is possible to conveniently and quickly determine the to-be-tested cable according to the time-spectrogram of the stress type and the quantitative relationship table between the PMD value and the matching metric. The force type of the external force received by the optical cable is measured, so as to determine the running state of the optical cable to be measured.

Description

A method and system for determining the operating state of an optical cable based on polarization mode dispersion

technical field

The present invention relates to the field of power communication optical cables in transmission lines and urban transmission channels, and more particularly, to a method and system for determining the operation state of optical cables based on polarization mode dispersion.

Background technique

While the power communication optical cable is developing vigorously, the phenomenon of external force damage is more prominent. At present, it is common that the operation defects of optical cables and optical fibers cannot be found in time. Basically, only when the optical fiber is interrupted, the location of the breakpoint can be found through the optical time domain reflectometer (OTDR) post-event test. Only a small number of optical cables are subjected to optical fiber stress testing, and the optical fiber cannot be On-line test and analysis are carried out on the health status of the operation of the optical cable and there are many emergencies, which cannot meet the requirements of condition maintenance.

The influence factors of external force on optical cable mainly include natural environment, human factors and accidental factors. The damage of external force will cause hidden dangers to the safe, reliable and healthy operation of the power communication network. For a long time, it mainly relies on fault handling or quality judgment after the fault occurs. The current technical means cannot comprehensively test the operation quality status of the optical fiber, cannot estimate the service life, and cannot provide a scientific basis for the maintenance and replacement of the optical cable. There are certain security risks in the communication network system. Therefore, there is a need for a method that can determine the operational status of an optical fiber cable.

SUMMARY OF THE INVENTION

The present invention provides a method and system for determining the operation state of an optical cable based on polarization mode dispersion (Polarization Mode Dispersion, PMD), so as to solve the problem of how to determine the type of external force received by the optical cable.

In order to solve the above problems, according to one aspect of the present invention, a method for determining the operating state of an optical cable based on polarization mode dispersion is provided, the method comprising:

Carry out polarization mode dispersion PMD value detection on the optical cable to be measured to obtain the real-time PMD value of the optical cable to be measured;

Compare the real-time PMD value of the optical cable to be measured with the preset PMD value and the PMD value range in the matching quantitative relationship table, determine the PMD value range corresponding to the real-time PMD value, and determine the PMD value according to the determined PMD value. The range determines the matching quantitative index of the optical cable to be tested;

According to the real-time PMD value of the optical cable to be tested and the matching quantification index of the optical cable to be tested, the force type is matched based on the preset force type time spectrogram, and the external force of the optical cable to be tested is determined. force type.

Preferably, the PMD value detection of the optical cable to be measured is performed to obtain the real-time PMD value of the optical cable to be measured, including:

The PMD value is detected on the optical cable to be tested according to the preset sampling times to obtain multiple PMD values, and the average value of the obtained multiple PMD values is calculated to obtain the real-time PMD value of the optical cable to be tested.

Preferably, in the preset PMD value and matching quantification relationship table, the PMD value range corresponds to the matching quantification index one-to-one, and with the increase of the PMD value range, the matching quantification corresponding to the PMD value range The indicator shows a monotonous growth trend.

Preferably, wherein the method further comprises:

Apply external forces of different stress types to multiple groups of optical cables to obtain the polarization mode dispersion PMD values of multiple groups of optical cables under different stress types, and perform statistical analysis on the obtained PMD values under different stress types to determine The time spectrum of the force type.

Preferably, the determined force type of the external force on the optical cable to be tested is: twisting, bending or crushing.

According to another aspect of the present invention, there is provided a system for determining the operating state of an optical cable based on polarization mode dispersion, the system comprising:

The real-time PMD value acquisition unit is used to detect the polarization mode dispersion PMD value of the optical cable to be measured, to obtain the real-time PMD value of the optical cable to be measured;

The matching quantification index determination unit is used to compare the real-time PMD value of the optical cable to be tested with the preset PMD value and the PMD value range in the matching quantification relationship table, and determine the PMD corresponding to the real-time PMD value value range, and determine the matching quantitative index of the optical cable to be tested according to the determined PMD value range;

The force type determination unit is used to match the force type according to the real-time PMD value of the optical cable to be measured and the matching quantification index of the optical cable to be measured, based on the preset force type time spectrogram, and determine the The force type of the external force on the cable under test.

Preferably, wherein the real-time PMD value determination unit performs PMD value detection on the optical cable to be measured to obtain the real-time PMD value of the optical cable to be measured, including:

The PMD value is detected on the optical cable to be tested according to the preset sampling times to obtain multiple PMD values, and the average value of the obtained multiple PMD values is calculated to obtain the real-time PMD value of the optical cable to be tested.

Preferably, in the preset PMD value and matching quantification relationship table, the PMD value range corresponds to the matching quantification index one-to-one, and with the increase of the PMD value range, the matching quantification corresponding to the PMD value range The indicator shows a monotonous growth trend.

Preferably, wherein the system further comprises:

The spectrogram determination unit under the force type is used to apply external forces of different force types to multiple groups of optical cables to obtain the polarization mode dispersion PMD values of multiple groups of optical cables under different force types, and to obtain different forces. Statistical analysis was performed on the PMD value under the type to determine the time spectrum of the force type.

Preferably, the determined force type of the external force on the optical cable to be tested is: twisting, bending or crushing.

The present invention provides a method and system for determining the operating state of an optical cable based on polarization mode dispersion, comprising: performing polarization mode dispersion PMD value detection on the optical cable to be measured to obtain the real-time PMD value of the optical cable to be measured; The real-time PMD value is compared with the preset PMD value and the matching quantitative relationship table, and the matching quantitative index of the optical cable to be measured is determined; according to the real-time PMD value of the optical cable to be measured and the The matching quantification index is used to match the force type based on the preset time spectrum of the force type, and determine the force type of the external force received by the optical cable to be tested. The method of the invention collects and analyzes the PMD value data under different working conditions through a large number of experiments, quantifies the PMD value and the matching degree of the optical fiber through intelligent calculation, forms a database, and comprehensively analyzes most of the external forces in the construction and operation of the optical fiber. Type, summarize and form a practical time spectrum diagram of force type, and propose a quantitative relationship table between PMD value and matching metric. The quantitative relationship table between PMD value and matching metric can easily and quickly determine the force type of the external force received by the optical cable to be tested, so as to determine the operating state of the optical cable to be tested.

Description of drawings

Exemplary embodiments of the present invention may be more fully understood by reference to the following drawings:

FIG. 1 is a flowchart of a method 100 for determining an operating state of an optical cable based on polarization mode dispersion according to an embodiment of the present invention;

FIG. 2 is a time spectrum diagram of a force type according to an embodiment of the present invention; and

FIG. 3 is a schematic structural diagram of a system 300 for determining an operating state of an optical cable based on polarization mode dispersion according to an embodiment of the present invention.

Detailed ways

Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, however, the present invention may be embodied in many different forms and is not limited to the embodiments described herein, which are provided for the purpose of this thorough and complete disclosure invention, and fully convey the scope of the invention to those skilled in the art. The terms used in the exemplary embodiments shown in the drawings are not intended to limit the invention. In the drawings, the same elements/elements are given the same reference numerals.

Unless otherwise defined, terms (including scientific and technical terms) used herein have the commonly understood meanings to those skilled in the art. In addition, it is to be understood that terms defined in commonly used dictionaries should be construed as having meanings consistent with the context in the related art, and should not be construed as idealized or overly formal meanings.

FIG. 1 is a flowchart of a method 100 for determining an operating state of an optical cable based on polarization mode dispersion according to an embodiment of the present invention. As shown in FIG. 1, the method for determining the operating state of an optical cable based on polarization mode dispersion provided by the embodiment of the present invention collects and analyzes PMD value data under different working conditions through a large number of experiments, and analyzes the PMD value and matching degree of the optical fiber through intelligent solution. Calculate the corresponding quantification, form a database, comprehensively analyze the types of most external forces in the construction and operation of the optical fiber cable, summarize and summarize the time spectrum when forming a practical force type, and propose a quantitative relationship table between the PMD value and the matching metric. After measuring the real-time PMD value of the cable, the force type of the external force received by the cable under test can be conveniently and quickly determined according to the time spectrum of the force type and the relationship table between the PMD value and the matching metric, so as to determine the cable under test. operating status. The method 100 for determining the operating state of an optical cable based on polarization mode dispersion determined by the embodiment of the present invention starts from step 101, and in step 101, the polarization mode dispersion PMD value detection of the optical cable to be measured is performed to obtain the real-time PMD value of the optical cable to be measured.

Preferably, the PMD value detection of the optical cable to be measured is performed to obtain the real-time PMD value of the optical cable to be measured, including:

The PMD value is detected on the optical cable to be tested according to the preset sampling times to obtain multiple PMD values, and the average value of the obtained multiple PMD values is calculated to obtain the real-time PMD value of the optical cable to be tested.

The ways and reasons for the damage of power communication cables by external forces are also different. The influence factors of the natural environment on the life of optical cables mainly include lightning strikes, icing, electrical corrosion, breeze vibration, galloping, etc., mainly for OPGW, ADSS and ordinary overhead optical cables. Human factors mainly include optical cable construction, municipal construction construction, irregular operation and maintenance, human damage, vehicle collision (stretching), etc. Other factors mainly include animal damage, misoperation, theft, etc.

However, after careful analysis and judgment, all types of external force events are mainly manifested in three types: bending, flattening, and twisting. Stretching mainly produces diameter shrinkage and creep of the optical cable, which also produces diameter shrinkage, and the force of external force impact to produce stretching is classified as flattening. applied to the inner fiber. External forces such as vibration and dancing are summarized as bending, including long-term and short-term external force application, instantaneous temperature rise such as lightning strike, and external mass increase such as icing. Torsion is mainly manifested in the construction process, including the construction of optical cables over pulleys and underground trenches. In this way, the various types of external force factors can be classified into three types: bending, squashing, and twisting.

The fiber is an anisotropic crystal, and a beam of light incident into the fiber is decomposed into two beams of refracted light. This phenomenon is the birefringence of light. If the optical fiber is an ideal situation, it means that its cross-section is not distorted, it is a complete true circle, and there is no stress in the core, and the optical fiber itself has no bending phenomenon. The refractive index of the beam transmitted in the axial direction of the fiber is unchanged, which is exactly the same as that of the isotropic crystal, and the PMD value is 0 at this time. However, the optical fiber in practical application is not ideal. Due to various reasons, the two polarization modes cannot be completely degenerate, resulting in polarization instability.

The reason for the instability of the polarization state of the light in the single-mode fiber, and different external forces will cause different polarization state changes, of course, more influencing factors come from the inside of the fiber (the fiber manufacturer uses the spinning rod method to change the fiber core ellipticity and asymmetric transverse stress). Parameters such as light intensity, polarization state (vector A) frequency and phase vary with the measurement state. However, when the external force causes the optical cable to bend and further affects the optical fiber, the PMD value exhibits a certain delay (the unit of the PMD value itself is ps, and the PMD value coefficient is Ps/km^1/2), And this delay under different external forces, the performance of the data is a function correlation, is a monotonic trend.

The measurement technology of PMD value has matured. Combined with the existing research results, it is shown that external factors such as bending and torsion of the finished optical cable due to construction and external forces have a certain impact on the PMD value of the optical fiber, but this effect is relatively small compared to the PMD value of the optical fiber itself. . In the analysis after a large amount of data collection, it is found that the law is related to the PMD value. The randomness provided can produce meaningful representations within different slopes. Especially in the time domain (the PMD value is mainly the time value), the trend presented by the algorithm can be optimized and can be used as the basis for judgment.

The basic characteristics of the PMD value coefficient of the polarization modality dispersion: the probability density distribution of the PMD value dispersion value in the optical fiber conforms to the Maxwell distribution, and the distribution function is:

Among them, the PMD value coefficient changes instantaneously with the change of wavelength, time, temperature and state. As a statistic sensitive to the environment, the PMD value test should try to keep the external environment stable. For fibers longer than 1 km, the PMD value is proportional to the square root of the length, taking into account the effect of mode coupling.

From the experimental data, it is concluded that for the optical fibers of the same optical cable, the birefringence and mode coupling caused by the internal structure are basically fixed. During the test, the state of the optical cable is unchanged, and the change points caused by the outside are stable. The temperature sensitivity of the PMD value coefficient is stable in the actual fiber optic cable. However, the PMD value has a certain volatility over time. Therefore, in the embodiment of the present invention, in order to ensure the statistical characteristics of the measurement, the test is performed every 1 hour, and the average value of the multiple measurements is obtained. Among them, the optical cable can be OPGW, ADSS, OPPC, ordinary overhead optical cable, pipeline optical cable, direct buried optical cable and in-station optical cable.

In step 102, the real-time PMD value of the optical cable to be measured is compared with the preset PMD value and the PMD value range in the matching quantitative relationship table, and the PMD value range corresponding to the real-time PMD value is determined, and according to The determined PMD value range determines the matching quantitative index of the optical cable to be tested.

Preferably, in the preset PMD value and matching quantification relationship table, the PMD value range corresponds to the matching quantification index one-to-one, and with the increase of the PMD value range, the matching quantification corresponding to the PMD value range The indicator shows a monotonous growth trend.

In the embodiment of the present invention, all stress situations are attributed to three stress modes, including: squashing, bending and torsion. Coupling the PMD value test data with these three modes, and integrating the matching function of the PMD value coefficients, the monotonicity of torsion < bending < flattening is realized. As the PMD value increases, the matching metric corresponding to the PMD value is monotonic. growth trend. The correspondence table between the PMD value and the matching metric is shown in Table 1. After the real-time PMD value is determined, the matching quantitative index corresponding to the real-time PMD value can be determined through Table 1.

Table 1 Quantitative relationship between PMD value and matching metric

In step 103, according to the real-time PMD value of the optical cable to be measured and the matching quantification index of the optical cable to be measured, based on the preset force type time spectrogram, the force type is matched, and it is determined that the optical cable to be measured is subjected to type of external force.

Preferably, wherein the method further comprises:

Apply external forces of different stress types to multiple groups of optical cables to obtain the polarization mode dispersion PMD values of multiple groups of optical cables under different stress types, and perform statistical analysis on the obtained PMD values under different stress types to determine The time spectrum of the force type.

Preferably, the determined force type of the external force on the optical cable to be tested is: twisting, bending or crushing.

In the embodiment of the present invention, through the realization data, it is further proposed that the main external force of the PMD value is torsional force in the stage of 0.050-0.201, bending force in the stage of 0.210-0.498, and flattening force in the stage of 0.501-0.997. force, forming matching spectra of at least three kinds of optical fibers of the cable. Since all types of forces have been summarized into these three modes, in practical engineering applications, when the above values appear, the matching charts and the spectrum maps are directly matched, so as to directly judge the construction and operation of the communication optical cable project. Dimension to establish security assurance methods. Among them, the torsion is actually manifested as the over-pulley during the construction process, and the galloping icing during the operation of the optical cable; the bending is manifested by the breeze vibration, wind deflection, lightning strike and other phenomena during operation; the flattening is mainly manifested by stretching and creep. and external impact, including tensile and stress strain. The time spectrum diagram of the force type of the embodiment of the present invention is shown in FIG. 2 . After the real-time PMD value and matching degree of the optical cable to be tested are determined, it can be matched with the time spectrum of the stress type to determine the stress type.

In the embodiment of the present invention, the optical cable is tested, wherein the optical cable model is OPGW-24B1+12ULL-240{267.5; 243.4}. The field conditions are as follows: Vibration test is carried out on the optical cable on a span of 60 meters, the tensile force of the optical cable reaches 60% RTS, the amplitude of the optical fiber reaches the standard required value, and the number of times reaches 10 ⁸ times. After about 70 million vibrations, the cable's bending strain has caused the fiber's dynamic stress to cause fatigue cracks in the fiber. First monitor the data in real time through the PMD value (the average sampling is greater than 3 times), and after displaying the PMD value (0.259), you can check the relationship table between the PMD value and the matching degree at the first time to determine the matching degree. Find the location in the area on the map and determine the type of external force that occurs.

FIG. 3 is a schematic structural diagram of a system 300 for determining an operating state of an optical cable based on polarization mode dispersion according to an embodiment of the present invention. As shown in FIG. 3 , the system 300 for determining the operating state of an optical cable based on polarization mode dispersion provided by an embodiment of the present invention includes: a real-time PMD value acquisition unit 301 , a matching quantification index determination unit 302 and a force type determination unit 303 .

Preferably, the real-time PMD value obtaining unit 301 is configured to perform polarization mode dispersion PMD value detection on the optical cable to be measured, so as to obtain the real-time PMD value of the optical cable to be measured.

Preferably, wherein the real-time PMD value determination unit 301 performs PMD value detection on the optical cable to be measured to obtain the real-time PMD value of the optical cable to be measured, including:

The PMD value is detected on the optical cable to be tested according to the preset sampling times to obtain multiple PMD values, and the average value of the obtained multiple PMD values is calculated to obtain the real-time PMD value of the optical cable to be tested.

Preferably, the matching quantification index determination unit 302 is configured to compare the real-time PMD value of the optical cable to be tested with the preset PMD value and the PMD value range in the matching quantification relationship table, and determine the The PMD value range corresponding to the real-time PMD value is determined, and the matching quantitative index of the optical cable to be tested is determined according to the determined PMD value range.

Preferably, in the preset PMD value and matching quantification relationship table, the PMD value range corresponds to the matching quantification index one-to-one, and with the increase of the PMD value range, the matching quantification corresponding to the PMD value range The indicator shows a monotonous growth trend.

Preferably, the force type determination unit 303 is configured to determine the force type based on the preset force type time spectrogram according to the real-time PMD value of the optical cable to be measured and the matching quantification index of the optical cable to be measured match, determine the force type of the external force on the optical cable to be tested.

Preferably, wherein the system further comprises:

The spectrogram determination unit under the force type is used to apply external forces of different force types to multiple groups of optical cables to obtain the polarization mode dispersion PMD values of multiple groups of optical cables under different force types, and to obtain different forces. Statistical analysis was performed on the PMD value under the type to determine the time spectrum of the force type.

Preferably, the determined force type of the external force on the optical cable to be tested is: twisting, bending or crushing.

The system 300 for determining the operating state of an optical cable based on polarization mode dispersion in the embodiment of the present invention corresponds to the method 100 for determining the operating state of an optical cable based on polarization mode dispersion in another embodiment of the present invention, and details are not described herein again.

The present invention has been described with reference to a few embodiments. However, as is known to those skilled in the art, other embodiments than the above disclosed invention are equally within the scope of the invention, as defined by the appended patent claims.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/the/the [means, component, etc.]" are open to interpretation as at least one instance of said means, component, etc., unless expressly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

As will be appreciated by those skilled in the art, the embodiments of the present application may be provided as a method, a system, or a computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) having computer-usable program code embodied therein.

The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the present application. It will be understood that each flow and/or block in the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to the processor of a general purpose computer, special purpose computer, embedded processor or other programmable data processing device to produce a machine such that the instructions executed by the processor of the computer or other programmable data processing device produce Means for implementing the functions specified in a flow or flow of a flowchart and/or a block or blocks of a block diagram.

These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory result in an article of manufacture comprising instruction means, the instructions The apparatus implements the functions specified in the flow or flow of the flowcharts and/or the block or blocks of the block diagrams.

These computer program instructions can also be loaded on a computer or other programmable data processing device to cause a series of operational steps to be performed on the computer or other programmable device to produce a computer-implemented process such that The instructions provide steps for implementing the functions specified in the flow or blocks of the flowcharts and/or the block or blocks of the block diagrams.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: the present invention can still be Modifications or equivalent replacements are made to the specific embodiments of the present invention, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention shall be included within the protection scope of the claims of the present invention.

Claims (8)

1. A method for determining the operating state of an optical cable based on polarization mode dispersion, wherein the method comprises: Carry out polarization mode dispersion PMD value detection on the optical cable to be measured to obtain the real-time PMD value of the optical cable to be measured; Compare the real-time PMD value of the optical cable to be measured with the preset PMD value and the PMD value range in the matching quantitative relationship table, determine the PMD value range corresponding to the real-time PMD value, and determine the PMD value according to the determined PMD value. The range determines the matching quantitative index of the optical cable to be tested; According to the real-time PMD value of the optical cable to be tested and the matching quantification index of the optical cable to be tested, the force type is matched based on the preset force type time spectrogram, and the external force of the optical cable to be tested is determined. force type; The method also includes: Apply external forces of different stress types to multiple groups of optical cables to obtain the polarization mode dispersion PMD values of multiple groups of optical cables under different stress types, and perform statistical analysis on the obtained PMD values under different stress types to determine The time spectrum of the force type. 2. method according to claim 1, is characterized in that, described optical cable to be measured is carried out PMD value detection, to obtain the real-time PMD value of described optical cable to be measured, comprising: The PMD value is detected on the optical cable to be tested according to the preset sampling times to obtain multiple PMD values, and the average value of the obtained multiple PMD values is calculated to obtain the real-time PMD value of the optical cable to be tested. 3. method according to claim 1, is characterized in that, in described preset PMD value and matching quantification relation table, PMD value range and matching quantification index are in one-to-one correspondence, and along with PMD value range increases, and the matching metric corresponding to the range of PMD values presents a monotonically increasing trend. 4 . The method according to claim 1 , wherein the determined force type of the external force on the optical cable to be tested is: twisting, bending or flattening. 5 . 5. A system for determining the operating state of an optical cable based on polarization mode dispersion, wherein the system comprises: The real-time PMD value acquisition unit is used to detect the polarization mode dispersion PMD value of the optical cable to be measured, to obtain the real-time PMD value of the optical cable to be measured; The matching quantification index determination unit is used to compare the real-time PMD value of the optical cable to be tested with the preset PMD value and the PMD value range in the matching quantification relationship table, and determine the PMD corresponding to the real-time PMD value value range, and determine the matching quantitative index of the optical cable to be tested according to the determined PMD value range; The force type determination unit is used for matching the force type according to the real-time PMD value of the optical cable to be measured and the matching quantification index of the optical cable to be measured, based on the preset force type time spectrogram, and determining the force type. The force type of the external force on the optical cable to be tested; The system also includes: The spectrogram determination unit under the force type is used to apply external forces of different force types to multiple groups of optical cables to obtain the polarization mode dispersion PMD values of multiple groups of optical cables under different force types, and to obtain different forces. Statistical analysis was performed on the PMD value under the type to determine the time spectrum of the force type. 6. system according to claim 5, is characterized in that, described real-time PMD value determination unit, carries out PMD value detection of optical cable to be measured, to obtain the real-time PMD value of described optical cable to be measured, comprising: The PMD value is detected on the optical cable to be tested according to the preset sampling times to obtain multiple PMD values, and the average value of the obtained multiple PMD values is calculated to obtain the real-time PMD value of the optical cable to be tested. 7. system according to claim 5, is characterized in that, in described preset PMD value and matching quantification relation table, PMD value range and matching quantification index are in one-to-one correspondence, and along with PMD value range increases, and the matching metric corresponding to the range of PMD values presents a monotonically increasing trend. 8 . The system according to claim 5 , wherein the determined force type of the external force on the optical cable to be tested is: twisting, bending or flattening. 9 .

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