CN113138065B - Device and method for analyzing few-mode fiber faults based on multi-mode transmission reflection - Google Patents

Device and method for analyzing few-mode fiber faults based on multi-mode transmission reflection Download PDF

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CN113138065B
CN113138065B CN202110400956.0A CN202110400956A CN113138065B CN 113138065 B CN113138065 B CN 113138065B CN 202110400956 A CN202110400956 A CN 202110400956A CN 113138065 B CN113138065 B CN 113138065B
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CN113138065A (en
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刘峰
张文萍
吴平
何振兴
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Wenzhou University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
    • G01M11/31—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter and a light receiver being disposed at the same side of a fibre or waveguide end-face, e.g. reflectometers
    • G01M11/3109—Reflectometers detecting the back-scattered light in the time-domain, e.g. OTDR
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
    • G01M11/33—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter being disposed at one fibre or waveguide end-face, and a light receiver at the other end-face
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
    • Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
    • Y04S10/00—Systems supporting electrical power generation, transmission or distribution
    • Y04S10/50—Systems or methods supporting the power network operation or management, involving a certain degree of interaction with the load-side end user applications
    • Y04S10/52—Outage or fault management, e.g. fault detection or location

Abstract

The invention provides a device for analyzing few-mode fiber faults based on multi-mode transmission reflection, which is used for connecting light emitting multiplexing equipment comprising a multi-path continuous light wave generating module, a ring light path module and a space mode conversion multiplexing and separating module and light receiving multiplexing equipment comprising a space mode separating module and an optical isolating module together on a tested few-mode fiber link. The device comprises a transmission power measurement module, a reflection/scattering power measurement module and a fault data processing and analyzing module, and the position of the fault of the few-mode optical fiber link to be detected is calculated mainly according to the transmission power and the total backscattering/reflecting power of different space modes before and after the fault of the few-mode optical fiber link to be detected. The method and the device are implemented to solve the problem that the current fault detection method cannot realize accurate fault detection of the few-mode optical fiber link, and have the advantages of real-time high efficiency, low cost, easiness in implementation and the like.

Description

Device and method for analyzing few-mode fiber faults based on multi-mode transmission reflection
Technical Field
The invention relates to the technical field of optical fiber fault detection, in particular to a device and a method for analyzing few-mode optical fiber faults based on multi-mode transmission reflection.
Background
With the increasing of communication services, people's demand for transmission capacity of communication systems is increasing, and various new technologies are emerging. Currently, a new generation of Mode Division Multiplexing (MDM) based few-Mode fiber (Few-Mode fiber, FMF) communication technology is favored. The technology utilizes the limited orthogonal mode in the few-mode optical fiber as an independent channel to carry out information transmission, can improve the transmission capacity of the system by times, breaks through the capacity limit of the traditional single-mode optical fiber system, and becomes a capacity expansion scheme which realizes the most competitive transmission capacity of Tbit/s and even Pbit/s of low-delay large-bandwidth 5G networks, access networks, data centers and the like. In recent years, the rapid development of the mode division multiplexing communication technology enables optical fiber communication to take a new step in the fields of ultra-large capacity, ultra-long distance and ultra-high speed. In the face of the rapid development of future few-mode fiber (FMF) research and development, network construction and application, a health monitoring technology matched with the FMF link is urgently needed to be developed in a coordinated manner, the reliability and stability of the FMF link are ensured, and economic loss and service quality reduction caused by high-capacity service interruption are avoided, so that the few-mode fiber link fault detection technology becomes more important.
At present, the fault detection of few-mode Optical fiber links is mainly a fault detection idea that continues single-mode Optical fiber links, and can be divided into two fault detection schemes, namely, Optical Time Domain Reflectometer (OTDR) and Optical Frequency Domain Reflectometer (OFDR). The above methods are all by measuring the fundamental mode LP 01 The characteristic is used for fault detection, and the fault detection and positioning of the single-mode optical fiber link can be better realized. For a few-mode fiber supporting multiple spatial modes, the failure loss characteristic of the high-order spatial mode and the fundamental mode LP 01 There is a large difference, only by measuring the fundamental mode LP 01 The characteristics are obviously inaccurate and not comprehensive. Therefore, the loss characteristics of each spatial mode need to be considered comprehensively, so that accurate characterization of the few-mode optical fiber link fault can be realized. Meanwhile, the modulation of the time domain or frequency domain signal brings some limitations, for example, for long-distance link fault detection, the optical time domain OTDR technology needs several minutes of averaging processing to obtain a stable backward rayleigh scattering distribution curve, and the fault detection efficiency is low; the optical frequency domain OFDR technology cannot realize longer-range fault detection due to the problem of the coherence length of a tunable light source; and complex modulated light sources are required, and the system cost is high.
Therefore, how to realize the fault detection and positioning of the few-mode optical fiber link with high efficiency, low cost, high dynamic range and high spatial resolution is a problem to be solved at present.
Disclosure of Invention
The technical problem to be solved by the embodiments of the present invention is to provide a device and a method for analyzing a few-mode fiber fault based on multi-mode transmission reflection, so as to solve the problem that the current fault detection method cannot realize accurate detection of the few-mode fiber link fault, and have the advantages of real-time high efficiency, low cost, easy implementation, and the like.
In order to solve the above technical problem, an embodiment of the present invention provides a device for analyzing few-mode fiber faults based on multi-mode transmission reflection, which is used for connecting a light emitting multiplexing device and a light receiving multiplexing device together on a measured few-mode fiber link; the optical transmission multiplexing equipment comprises a multi-path continuous light wave generation module, an annular light path module and a spatial mode conversion multiplexing and separating module which are sequentially connected; the light receiving multiplexing equipment comprises a spatial mode separation module and an optical isolation module which are connected in sequence;
the device comprises a transmission power measuring module, a reflection/scattering power measuring module and a fault data processing and analyzing module; wherein the content of the first and second substances,
the input end of the transmission power measuring module is connected with the optical isolation module, the output end of the transmission power measuring module is connected with the fault data processing and analyzing module, and the transmission power measuring module is used for measuring transmission power output by two optical isolators in the optical isolation module and comprises transmission power of each space mode before and after a tested few-mode optical fiber link fails;
the input end of the reflection/scattering power measurement module is connected with both the two single-mode fiber circulators in the annular light path module, and the output end of the reflection/scattering power measurement module is connected with the fault data processing and analyzing module, and is used for measuring the reflection/scattering power output by the two single-mode fiber circulators in the annular light path module, including the total backscattering/reflecting power of each spatial mode before and after the fault of the measured few-mode fiber link;
and the fault data processing and analyzing module is used for calculating the fault position of the few-mode optical fiber link to be detected according to the transmission power and the total backscattering/reflecting power of the few-mode optical fiber link to be detected before the fault occurs, and the transmission power and the total backscattering/reflecting power of the few-mode optical fiber link to be detected after the fault occurs.
The multi-path continuous light wave generating module comprises a single-frequency laser light source and a light beam splitter which are connected in sequence; wherein the content of the first and second substances,
the single-frequency laser light source is used for emitting continuous light waves with the central wavelength of 1550nm, and the power is adjustable;
the optical beam splitter is connected with the two single-mode optical fiber circulators in the annular light path module and is used for dividing continuous light waves output by the single-frequency laser light source into two paths to be output to the two single-mode optical fiber circulators.
Wherein, the transmission power P before the failure of the tested few-mode optical fiber link T0i Is shown as
Figure BDA0003020261390000031
Wherein the content of the first and second substances,
P 0i two paths of continuous input power generated by the multi-path continuous light wave generating module are represented as 1 or 2; IL cir(12i) The insertion loss between the two single-mode optical fiber circulators in the annular optical path module and the spatial mode conversion multiplexing and separating module is measured; IL iso(i) The insertion loss of two optical isolators in the optical isolator module; IL MUX(i) An insertion loss of the multiplexing and demultiplexing module for the spatial mode conversion; IL DMUX(i) Is the insertion loss of the spatial mode splitting module; t is i (L) is the measured transmission coefficient of the few-mode fiber link mode, which can be expressed as:
Figure BDA0003020261390000032
α i is the mode loss factor.
Wherein, the transmission power P of the tested few-mode optical fiber link after failure Ti Is shown as
Figure BDA0003020261390000033
Wherein, the total back scattering/reflection power P before the failure of the tested few-mode optical fiber link B0i Is shown as
Figure BDA0003020261390000034
Wherein IL cir(23i) Is a stand forThe insertion loss between two single-mode optical fiber circulators in the annular optical path module and the reflection/scattering power measurement module; RAY i (L) is the coefficient of the back Rayleigh scattering power, which can be expressed as
Figure BDA0003020261390000041
α si Is a back Rayleigh scattering coefficient, B i,i Is the fiber backscatter capture coefficient.
Wherein, the total back scattering/reflection power P after the failure of the tested few-mode optical fiber link Bi Is shown as
Figure BDA0003020261390000042
Wherein the power reflection coefficient R is normalized i Can be expressed as
Figure BDA0003020261390000043
The embodiment of the invention also provides a method for analyzing few-mode fiber faults based on multi-mode transmission reflection, which is realized on the device for analyzing few-mode fiber faults based on multi-mode transmission reflection, and the method comprises the following steps:
receiving the transmission power of each space mode before and after the fault of the tested few-mode optical fiber link;
receiving total backscattering/reflection power of each space mode before and after a fault occurs to a tested few-mode optical fiber link;
and calculating the position of the few-mode optical fiber link to be detected with faults according to the transmission power and the total backscattering/reflecting power of each space mode before the few-mode optical fiber link to be detected with faults and the transmission power and the total backscattering/reflecting power of each space mode after the few-mode optical fiber link to be detected with faults.
The embodiment of the invention has the following beneficial effects:
1. according to the invention, the accurate detection and positioning of the fault event can be realized only by injecting continuous light waves into the corresponding space mode of the few-mode optical fiber and measuring and quantitatively analyzing the transmission power and the scattering/reflecting power of different space modes before and after the fault occurs, and the system has the advantages of low cost, simplicity, effectiveness and easiness in realization;
2. the invention only needs to analyze the transmission power and the scattering/reflecting power value through the quantization, does not need to be averaged, and has real-time and high-efficiency detection;
3. the invention can improve the measuring range by adjusting the power of the continuous light waves injected into different space modes, does not influence the positioning precision and realizes the double advantages of space resolution and dynamic range.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is within the scope of the present invention for those skilled in the art to obtain other drawings based on the drawings without inventive exercise.
Fig. 1 is a schematic structural diagram of an apparatus for analyzing few-mode fiber faults based on multi-mode transmission reflection according to an embodiment of the present invention;
fig. 2 is an application scenario of a device for analyzing few-mode fiber faults based on multi-mode transmission reflection according to an embodiment of the present invention, where 3-mode fibers are used as an example to simulate different positions z of a few-mode fiber link p Upon introduction of a fault event, the spatial mode LP 01 Normalized power reflection coefficient R 01 A variation graph;
fig. 3 is an application scenario of a device for analyzing a few-mode fiber fault based on multi-mode transmission reflection according to an embodiment of the present invention, where a 3-mode fiber is used as an example to simulate different positions z of a few-mode fiber link p Upon introduction of a fault event, the spatial pattern LP 11 Normalized power reflection coefficient R 11 A variation graph;
fig. 4 is a flowchart of a method for analyzing few-mode fiber faults based on multi-mode transmission reflection according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings.
As shown in fig. 1, in an embodiment of the present invention, an apparatus for analyzing few-mode fiber faults based on multi-mode transmission reflection is provided, which is used for connecting an optical transmission multiplexing device and an optical reception multiplexing device together on a measured few-mode fiber link 104; the optical transmission multiplexing device comprises a multi-path continuous light wave generation module 101, an annular light path module 102 and a spatial mode conversion multiplexing and separating module 103 which are connected in sequence; the optical receiving multiplexing device comprises a spatial mode separation module 105 and an optical isolation module 106 which are connected in sequence;
the device comprises a transmission power measurement module 107, a reflection/scattering power measurement module 108 and a fault data processing and analyzing module 109; wherein the content of the first and second substances,
the input end of the transmission power measurement module 107 is connected with the optical isolation module 106, and the output end of the transmission power measurement module is connected with the fault data processing and analyzing module 109, and is used for measuring transmission power output by two optical isolators 1061 and 1062 in the optical isolation module 106, including transmission power before and after a fault occurs in a measured few-mode optical fiber link;
the input end of the reflected/scattered power measurement module 108 is connected to both the two single-mode fiber circulators 1021 and 1022 in the annular optical path module 102, and the output end is connected to the failure data processing and analyzing module 109, and is used for measuring the reflected/scattered power output by both the two single-mode fiber circulators 1021 and 1022 in the annular optical path module 102, including the total backscatter/reflected power of each spatial mode before and after the failure of the measured few-mode fiber link;
and the fault data processing and analyzing module 109 is configured to calculate a fault position of the measured few-mode fiber link according to the transmission power and the total backscattering/reflection power before the measured few-mode fiber link fails, and the transmission power and the total backscattering/reflection power of each spatial mode after the measured few-mode fiber link fails.
In the embodiment of the present invention, the multi-channel continuous light wave generating module 101 comprises a plurality of sequential light wavesThe single-frequency laser light source and the optical beam splitter are connected; the single-frequency laser light source is used for emitting continuous light waves with the center wavelength of 1550nm, and the power is adjustable, that is, the fault location of the measured few-mode optical fiber link 104 in different dynamic ranges can be realized by adjusting the power of the single-frequency laser light source; the optical splitter is connected to both single-mode fiber ring 1021 and 1022 in the ring optical path module 102, and is configured to split the continuous light wave output from the single-frequency laser light source into two paths, and output the two paths to the two single-mode fiber ring 1021 and 1022, where the two paths are P in size, respectively 01 And P 02 。
At this time, two continuous optical wave signals output by the optical splitter are respectively input through ports 1 of two single mode fiber circulators 1021 and 1022, output through ports 2, and output by LP m And LP n The port enters a spatial mode conversion multiplexing and separating module 103; meanwhile, the reflected/scattered signals spatially separated by the spatial mode conversion multiplexing and separating module 103 are provided by the LP m And LP n The ports enter single mode fiber circulators 1021 and 1022 in the ring optical path module 102, port 2, and exit port 3 into the reflected/scattered power measurement module 108. The spatial mode conversion multiplexing and separating module 103 respectively implements spatial mode conversion multiplexing and spatial mode separation by forward and backward use, and specifically, the forward use is mainly used for two paths of signals (output by the fundamental mode LP) output by the ports 2 of the single-mode fiber circulators 1021 and 1022 in the ring optical path module 102 01 Mode-bearing continuous lightwaves) for spatial mode conversion into corresponding LPs m And LP n Spatial mode and multiplexing injection into the tested few-mode fiber link 104; the reverse use primarily performs spatial mode separation on the reflected/scattered signals generated in the measured few-mode fiber link 104.
One end of the tested few-mode optical fiber link 104 is connected with the spatial mode conversion multiplexing and separating module 103 output pigtail, the other end is connected with the spatial mode separating module 105 few-mode pigtail, and the fault position is z P . The spatial mode separation module 105 mainly separates the multiplexing spatial mode transmitted by the measured few-mode fiber link 104 to obtain LP m And LP n Mode-carried continuous optical signal, LP m And LP n The ports are connected to optical isolator 1061 and 1062 input ports in optical isolation module 106, respectively.
Optical isolation module 106 is comprised of optical isolators 1061 and 1062 to minimize reflections off the end faces of the fiber ends, and the outputs of optical isolators 1061 and 1062 are connected to reflected/scattered power measurement module 107.
The transmission power measurement module 107 measures the transmission power output by the optical isolation module 106, including the transmission power P before and after the failure of the measured few-mode optical fiber link 104 T0 、P T 。
The reflected/scattered power measurement module 108 measures the reflected/scattered power output by the ports 3 of the two single-mode fiber circulators 1021 and 1022 in the ring-shaped optical path module 102, wherein the reflected/scattered power includes the reflected/scattered power P before and after the failure of the measured few-mode fiber link 104 B0 、P B 。
The failure data processing and analyzing module is connected with the transmission power measuring module 107 and the reflection/scattering power measuring module 108, and analyzes the transmission power P before and after the few-mode optical fiber link fails T0 、P T And reflected/scattered power P B0 、P B And the accurate positioning of the tested few-mode optical fiber link 104 is realized.
In the embodiment of the present invention, firstly, the transmission power and the reflection/scattering power of the few-mode optical fiber link 104 before the failure need to be measured, specifically:
(I) transmission power P before failure of measured few-mode optical fiber link 104 T0i That is, when no fault occurs in the measured few-mode optical fiber link 104, the transmission power P before the fault is measured by the transmission power measurement module 107 T0i (i＝1@LP m ,i＝2@LP n ) Can be expressed as:
Figure BDA0003020261390000081
wherein, P 0i The input power is two continuous input powers generated by the multi-path continuous light wave generating module 101, i is 1 or 2; IL cir(12i) For two single modes in the annular optical path module 102The insertion loss between the fiber circulators 1021 and 1022 to the spatial mode conversion multiplexing and demultiplexing module 103 (i.e., port 1 to port 2) is in dB; IL iso(i) The insertion loss in dB for the two optical isolators 1061 and 1062 in the optical isolator module 106; IL MUX(i) The insertion loss in dB for the spatial mode conversion multiplexing and demultiplexing module 103; IL DMUX(i) The module 105 is separated for spatial modes (i.e., LP) m And LP n Ports) in dB; t is i (L) is the mode transmission coefficient of the measured few-mode fiber link 104, which can be expressed as:
Figure BDA0003020261390000082
α i as the mode loss coefficient, the loss coefficient alpha of different space modes of the tested few-mode optical fiber i Different, resulting in different modes of transmission coefficient T i (L) have certain differences.
(II) Total Back-scattered/reflected Power P before failure of the measured few-mode fiber Link 104 B0i That is, when no failure event occurs in the measured few-mode fiber link 104, the directivities DIR of the two single-mode fiber circulators 1021 and 1022 in the annular optical path module 102 are considered i (i.e., power transmitted directly from port 1 to port 3), return loss RL of the two optical isolators 1061, 1062 in the optical isolation module 106 iso(i) Spatial mode conversion multiplexing and separation module 103 return loss RL MUX(i) Return loss RL of the spatial mode separation module 105 MUX(i) And the back Rayleigh scattering power generated in the measured few-mode optical fiber link 104, and the back Rayleigh scattering power is measured by a reflection/scattering power measurement module 108 to obtain P B0i Can be expressed as
Figure BDA0003020261390000091
Wherein IL cir(23i) The insertion loss between the two single-mode fiber circulators 1021 and 1022 in the annular optical path module 102 to the reflected/scattered power measurement module 108 (i.e., port 2 to port 3) is expressed in dB; RAY i (L) is the coefficient of the back Rayleigh scattering power, canIs expressed by the formula (3) as
Figure BDA0003020261390000092
Wherein alpha is si Is the back Rayleigh scattering coefficient, B i,i Is the fiber backscatter capture coefficient.
Secondly, the transmission power and the reflection/scattering power of the few-mode fiber link 104 after the failure need to be measured, specifically:
(III) Transmission Power P after failure of the measured few-mode fiber Link 104 Ti I.e. at the position z of the measured few-mode fiber link 104 P When a fault event occurs, the insertion loss introduced by the fault event is set to IL i The return loss is RL, where RL is defined as: 10 log 10 (η), η is the ratio of the input power to the reflected power. The transmission power P is measured by the transmission power measurement module 107 Ti (i＝1@LP m ,i＝2@LP n ) It can be expressed as:
Figure BDA0003020261390000093
at this time, by measuring the transmission power P Ti And P T0i Insertion loss IL of failure event of measured few-mode fiber link 104 i Can be calculated from equation (4).
(IV) Total Back-scattered/reflected Power P after failure of the measured few-mode fiber Link 104 Bi At position z of the measured few-mode fiber link 104 P When a fault event occurs, the total back scattering/reflection power P is measured by the reflection/scattering power measurement module 108 Bi Can be expressed as
Figure BDA0003020261390000101
The normalized power reflection coefficient R can be calculated from the equations (2) and (5) i Can be expressed as:
Figure BDA0003020261390000102
from (I) to (IV), it is clear that DIR is caused by i 、IL cir12(23)i 、RL iso(i) 、RL MUX(i) And RL DMUX(i) Is a known parameter and crosses alpha i 、L、IL i 、P B0i 、P Bi A value of a parameter obtained by preliminary measurement, alpha si ·B i.i Can be obtained by calculation of formula (2).
Therefore, the problem of locating and quantitatively characterizing the fault event of the measured few-mode optical fiber link 104 is converted into a fault solution containing an unknown parameter z P And RL equation set (i.e., equation (6) i ═ 1@ LP m ,i＝2@LP n ) Is to measure the resulting R 1 And R 2 Substituting into formula (6), performing data processing analysis by the fault data processing and analyzing module 109, and solving the value of z by least square method P And RL value, realize the accurate positioning and characterization of the few-mode fiber link 104 fault event of being surveyed.
It can be understood that the multimode measurement can be extended on the basis of the above, that is, a plurality of suitable multiplexing spatial modes are selected as transmission reflection analysis objects (specifically, according to the loss characteristic analysis of each spatial mode, the selection has higher fault sensitivity characteristic, and simultaneously, the selection of degenerate mode is avoided as much as possible), so as to realize the fault event occurrence position z P And (4) accurate calculation.
As shown in fig. 2 to fig. 3, an application scenario of the apparatus for analyzing few-mode fiber faults based on multi-mode transmission reflection provided in the embodiment of the present invention is further described:
mode coupling coefficients and mode coupling profiles were measured for a 3-mode fiber that supported three modes, LP01, LP11a, and LP11 b.
In the simulation experiment, the graded-index 3-mode optical fiber is taken as an example, and LP01 (alpha) is provided i ＝0.19dB/km,B i,i ＝0.00175，α si 0.169dB/km) and LP11 (alpha) i ＝0.20dB/km,B i,i ＝0.00196，α si 0.169dB/km) twoA spatial mode, which takes 10dB of insertion loss into consideration and is set at the position of few-mode optical fiber link failure to be changed into z p (0-L); the change range of the return loss RL is 20dB to 80 dB; the directivity DIR of the fiber optic circulator is 60 dB; return loss RL of isolator iso Is 65 dB; the length L of the few-mode optical fiber link is 6 km. When no fault event occurs in the few-mode optical fiber link, the total backscattering/reflecting power P is obtained by system measurement B0i Measuring the back scattering/reflection power P when the few-mode optical fiber link fails Bi The ratio normalized power reflection coefficient R of different space modes between back scattering/reflection before and after the fault occurs can be obtained i FIG. 2 and FIG. 3 show normalized power reflection coefficients R for different fault location spatial modes LP01 and LP11 01 And R 11 The graph is varied.
From the simulation results, R 01 And R 11 Location z with event p And a change in return loss RL. For fixed RL and z p Only unique (R) 01 ，R 11 ) The points correspond to the points. Thus, by measuring R 01 And R 11 And quantitatively analyzing the transmission power and the scattering/reflecting power of different space modes before and after the fault occurs, and calculating corresponding and unique z p And the method can accurately represent and position the few-mode optical fiber link fault event, thereby proving the feasibility of the theoretical model.
As shown in fig. 4, in an embodiment of the present invention, a method for analyzing a few-mode fiber fault based on multi-mode transmission reflection is provided, which is implemented on the apparatus for analyzing a few-mode fiber fault based on multi-mode transmission reflection, and the method includes the following steps:
step S1, receiving the transmission power of each space mode before and after the failure of the tested few-mode optical fiber link;
step S2, receiving total backscattering/reflection power of each space mode before and after the failure of the tested few-mode optical fiber link;
and step S3, calculating the position of the few-mode optical fiber link to be detected at which the fault occurs according to the transmission power and the total backscattering/reflection power of each space mode before the few-mode optical fiber link to be detected fails and the transmission power and the total backscattering/reflection power of each space mode after the few-mode optical fiber link to be detected fails.
The embodiment of the invention has the following beneficial effects:
1. according to the invention, the accurate detection and positioning of the fault event can be realized only by injecting continuous light waves into the corresponding space mode of the few-mode optical fiber and measuring and quantitatively analyzing the transmission power and the scattering/reflecting power of different space modes before and after the fault occurs, and the system has the advantages of low cost, simplicity, effectiveness and easiness in realization;
2. the invention only needs to analyze the transmission power and the scattering/reflecting power value through the quantization, does not need to be averaged, and has real-time and high-efficiency detection;
3. the invention can improve the measuring range by adjusting the power of the continuous light waves injected into different space modes, does not influence the positioning precision and realizes the double advantages of space resolution and dynamic range.
It will be understood by those skilled in the art that all or part of the steps in the method for implementing the above embodiments may be implemented by relevant hardware instructed by a program, and the program may be stored in a computer-readable storage medium, such as ROM/RAM, magnetic disk, optical disk, etc.
The above disclosure is only for the purpose of illustrating the preferred embodiments of the present invention, and it is therefore to be understood that the invention is not limited by the scope of the appended claims.

Claims (7)

1. A device for analyzing few-mode fiber faults based on multi-mode transmission reflection is characterized by being used on a tested few-mode fiber link for connecting light emitting multiplexing equipment and light receiving multiplexing equipment together; the optical transmission multiplexing equipment comprises a multi-path continuous light wave generation module, an annular light path module and a spatial mode conversion multiplexing and separating module which are sequentially connected; the light receiving multiplexing equipment comprises a space mode separation module and an optical isolation module which are sequentially connected;
the device comprises a transmission power measuring module, a reflection/scattering power measuring module and a fault data processing and analyzing module; wherein the content of the first and second substances,
the input end of the transmission power measuring module is connected with the optical isolation module, the output end of the transmission power measuring module is connected with the fault data processing and analyzing module, and the transmission power measuring module is used for measuring transmission power output by two optical isolators in the optical isolation module and comprises transmission power of each space mode before and after a fault occurs in a measured few-mode optical fiber link;
the input end of the reflection/scattering power measurement module is connected with both the single-mode fiber circulators in the annular light path module, and the output end of the reflection/scattering power measurement module is connected with the fault data processing and analyzing module, and the reflection/scattering power measurement module is used for measuring the reflection/scattering power output by the two single-mode fiber circulators in the annular light path module and comprises the total backscattering/reflecting power of each space mode before and after the fault of the measured few-mode fiber link;
and the fault data processing and analyzing module is used for calculating the fault position of the few-mode optical fiber link to be detected according to the transmission power and the total backscattering/reflecting power of each space mode before the few-mode optical fiber link to be detected fails and the transmission power and the total backscattering/reflecting power of each space mode after the few-mode optical fiber link to be detected fails.
2. The apparatus for analyzing few-mode fiber faults based on multi-mode transmission reflection according to claim 1, wherein the multi-path continuous light wave generating module comprises a single-frequency laser light source and a light beam splitter connected in sequence; wherein the content of the first and second substances,
the single-frequency laser light source is used for emitting continuous light waves with the central wavelength of 1550nm, and the power is adjustable;
the optical beam splitter is connected with the two single-mode optical fiber circulators in the annular light path module and is used for dividing continuous light waves output by the single-frequency laser light source into two paths to be output to the two single-mode optical fiber circulators.
3. The multi-mode transmission-based system of claim 1The device for analyzing the few-mode fiber fault through reflection is characterized in that the transmission power P of the tested few-mode fiber link before the fault occurs T0i Is shown as
Figure FDA0003720528980000021
Wherein the content of the first and second substances,
P 0i two paths of continuous input power generated by the multi-path continuous light wave generating module are represented as 1 or 2; IL cir(12i) The insertion loss between the two single-mode optical fiber circulators in the annular optical path module and the spatial mode conversion multiplexing and separating module is measured; IL iso(i) The insertion loss of two optical isolators in the optical isolator module; IL MUX(i) An insertion loss of the multiplexing and demultiplexing module for the spatial mode conversion; IL DEMUX(i) An insertion loss of the spatial mode separation module; t is i (L) is the transmission coefficient of the tested few-mode optical fiber link mode, and is expressed as:
Figure FDA0003720528980000024
α i is the mode loss factor.
4. The apparatus according to claim 3, wherein the transmission power P of the tested few-mode fiber link after failure is higher than the transmission power P of the tested few-mode fiber link after failure Ti Is shown as
Figure FDA0003720528980000022
5. The apparatus according to claim 4, wherein the total back-scattered/reflected power P of each spatial mode before the failure of the tested few-mode fiber link is determined according to the transmission reflection analysis B0i Is shown as
Figure FDA0003720528980000023
Wherein IL cir(23i) The insertion loss between two single-mode optical fiber circulators in the annular optical path module and the reflection/scattering power measurement module is measured; RAY i (L) is the coefficient of the back Rayleigh scattering power, expressed as
Figure FDA0003720528980000031
α si Is a back Rayleigh scattering coefficient, B i,i Is the fiber backscatter capture coefficient.
6. The apparatus according to claim 5, wherein the total backscattering/reflected power P after the failure of the tested few-mode fiber link is larger than the total backscattering/reflected power P Bi Is shown as
Figure FDA0003720528980000032
Wherein the power reflection coefficient R is normalized i Is shown as
Figure FDA0003720528980000033
7. A method for analyzing few-mode fiber faults based on multi-mode transmission reflection, which is implemented on the apparatus for analyzing few-mode fiber faults based on multi-mode transmission reflection according to claim 6, the method comprising the following steps:
receiving the transmission power of each space mode before and after the failure of the tested few-mode optical fiber link;
receiving total backscattering/reflection power of each space mode before and after a fault occurs to a tested few-mode optical fiber link;
and calculating the position of the few-mode optical fiber link to be detected with faults according to the transmission power and the total backscattering/reflecting power of each space mode before the few-mode optical fiber link to be detected with faults and the transmission power and the total backscattering/reflecting power of each space mode after the few-mode optical fiber link to be detected with faults.
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