System and method for measuring insertion loss and return loss of multi-core optical fiber link based on OFDR (Optical Frequency Domain Reflectometer)

Abstract

The invention provides a system and a method for measuring insertion loss and return loss of a multi-core optical fiber link based on an OFDR (Optical Frequency Domain Reflectometer), and belongs to the field of optical fiber link diagnosis and measurement. The system is composed of a multi-wavelength laser, three wavelength division multiplexers, two couplers, N circulators, a photoelectric detector, a data acquisition card, a to-be-measured link and an upper computer, the multi-wavelength laser outputs laser with N wavelengths, the wavelength division multiplexers multiplex signals and then divide the signals into signal light and reference light through a first coupler, the signal light is used for being output to the to-be-measured link, and the reference light is used for being output to the to-be-measured link. A mixing signal formed by the reflected light of the to-be-measured link and the reference light interferes in the photoelectric detector, a coherent mixing signal containing the insertion loss and return loss information of the to-be-measured link is measured, and the insertion loss and return loss of each node of the to-be-measured link can be calculated by analyzing the coherent mixing signal. By using the OFDR technology, the full-range measurement from the starting point to the ending point of the optical fiber is realized, so that the OFDR can comprehensively diagnose the health state of the optical fiber link.

Description

Technical Field

[0001] The present invention belongs to the field of optical fiber link diagnosis and measurement, and particularly relates to a measurement system and method for insertion loss and return loss of multi-core optical fiber links based on OFDR. Background Art

[0002] With the rapid development of information technology, optical fiber communication systems have occupied a core position in the global communication network. To meet the increasing demand for data traffic, optical fiber transmission systems are constantly evolving towards higher bandwidth, larger capacity, and lower loss. Multi-core fiber (MCF) technology, as an emerging solution, can integrate multiple transmission cores in one optical fiber, significantly improving the transmission capacity of the optical fiber. MPO (Multi-Fiber Push On), a high-density optical fiber bundle connection method, supports simultaneous transmission of multiple data channels and has become the standard connector in data centers and communication systems. The MCF-MPO system combines MCF and MPO to form a new type of space division multiplexing technology, whose advantage lies in its ability to integrate multiple optical signal channels in a limited space, thereby greatly improving the bandwidth utilization rate and connection density. At the same time, optical frequency domain reflectometry (OFDR) is a high-precision optical fiber link detection technology. Compared with the prior art, OFDR can obtain the complete information of the link, thereby realizing the accurate measurement of optical fiber loss, fault location, and other important optical characteristics.

[0003] However, traditional loss measurement systems mostly adopt single-wavelength measurement methods. Although suitable for simple fiber optic connector measurements, when dealing with multi-core, complex structures containing MPO links, single-wavelength systems cannot meet the comprehensive monitoring requirements of multi-channel signals. On the other hand, single-wavelength systems cannot conduct comprehensive real-time monitoring of the entire fiber optic link like distributed measurement systems. Distributed measurement technology can simultaneously perform loss measurements across the entire link range, avoiding the limitation of single-wavelength systems that can only perform limited measurements on a certain part or a certain channel. For example, in high-speed fiber optic communication environments such as data centers, the measurement efficiency of multi-channel systems directly affects the deployment and maintenance speed of the network, especially when quickly diagnosing and troubleshooting large-scale networks. The measurement of insertion loss and return loss usually relies on an optical power meter combined with an optical switch to measure the transmitted and reflected optical powers of each fiber core by switching cores one by one. However, this method has obvious disadvantages. The optical power meter can only provide information on the overall link loss, unable to locate the specific location where the loss occurs (such as contamination of the connector end face, micro-cracks at bending points), and is easily affected by light source fluctuations, environmental temperature changes, and the surface reflectivity of the object under test. Although power ratio compensation is required to eliminate common-mode noise, there are still errors. Therefore, there is currently a lack of dedicated measurement technologies for insertion loss and return loss in MCF-MPO links. Summary of the Invention

[0004] To solve the above problems, a measurement system and method for insertion loss and return loss of multi-core fiber optic links based on OFDR are designed to efficiently and accurately calculate insertion loss and return loss, and improve the fault location efficiency.

[0005] The technical solution adopted by the embodiments of the present invention to solve its technical problems is:

[0006] A measurement system for insertion loss and return loss of multi-core fiber optic links based on OFDR, comprising:

[0007] A multi-wavelength laser (100), a first wavelength division multiplexer (210a), a second wavelength division multiplexer (210b), a third wavelength division multiplexer (210c), a first coupler (220a), a second coupler (220b), N circulators (230-n), a photodetector (240), a data acquisition card (250), a link under test, and a host computer (400);

[0008] The multi-wavelength laser (100) simultaneously provides laser signals of N wavelengths to the first wavelength division multiplexer (210a);

[0009] The first wavelength division multiplexer (220a) has N input ports and 1 output port, combines the received laser signals and outputs them to the first coupler (220a);

[0010] The first coupler (220a) has 1 input port and 2 output ports, splits the received optical signal into signal light and reference light, outputs the signal light to the second wavelength division multiplexer (210b), and outputs the reference light to the second coupler (220b);

[0011] The second wavelength division multiplexer (210b) has 1 input port and N output ports, separates the multiplexed and transmitted signal light into N original signal lights with different wavelengths and outputs them to N circulators (230-n);

[0012] Each of the N circulators (230-n) has 3 ports, outputs the N original signal lights to the link under test respectively, and receives the reflected light from the link under test and transmits it to the third wavelength division multiplexer (210c), and the reflected light is backward Rayleigh scattering light;

[0013] The link under test consists of a multi-core fiber fan-in / fan-out device (310), A multi-core fibers, and A multi-core fiber connectors (320); The N circulators (230-n) are connected to the N input ports of the multi-core fiber fan-in / fan-out device (310) through single-core fibers, and the A multi-core fiber connectors (320) and the A multi-core fibers are alternately connected. Among them, the first multi-core fiber at the end point is connected to the output port of the multi-core fiber fan-in / fan-out device (310); After the N original signal lights of the N circulators (230-n) enter the multi-core fiber fan-in / fan-out device (310), N reflected lights are generated in the link under test and enter the N circulators (230-n) through the multi-core fiber fan-in / fan-out device (310);

[0014] The third wavelength division multiplexer (210c) has N input ports and 1 output port, combines the received N reflected lights and outputs them to the second coupler (220b);

[0015] The second coupler (220b) has 2 input ports and 1 output port, mixes the reference light from the first coupler (220a) and the reflected light received from the third wavelength division multiplexer (210c) into a mixed signal and outputs it to the photodetector (240);

[0016] The mixed signal interferes in the photodetector (240) to obtain a coherent mixed signal containing the insertion loss and return loss information of the link under test. The photodetector (240) converts the coherent mixed signal into an electrical signal and outputs it to the data acquisition card (250);

[0017] The data acquisition card (250) converts the electrical signal into a digital signal and transmits it to the host computer (400);

[0018] The host computer (400) calculates the insertion loss and return loss of each node of the link under test based on the digital signal.

[0019] Preferably, the multi-wavelength laser is configured to simultaneously provide swept-frequency light of multiple wavelengths.

[0020] Preferably, the coupling ratio of the first coupler (220a) is 1:99, and the coupling ratio of the second coupler (220b) is 50:50.

[0021] Preferably, let the A-th multi-core fiber connector (320-a) located at the end of the link to be measured and the A-th multi-core fiber connection point be node g, where g ∈ [1, G] and G = 2A, and the connection point of the first multi-core fiber and the multi-core fiber fan-in / fan-out unit (310) be node 1.

[0022] Preferably, the multi-core fiber is composed of multiple multi-core fibers, a spiral armor sleeve, an inner sheath, aramid, and an outer sheath from the inside to the outside in sequence.

[0023] The present invention provides a method for measuring the insertion loss and return loss of a multi-core fiber link based on OFDR, and the implementation subject is the aforementioned measurement system for the insertion loss and return loss of a multi-core fiber link based on OFDR; the steps include:

[0024] Step S1, build a measurement system for the insertion loss and return loss of a multi-core fiber link based on OFDR;

[0025] Step S2, the multi-wavelength laser (100) emits optical signals f of N frequencies n , which enter the first coupler (220a) through the first wavelength division multiplexer (210a) and are divided into signal light and reference light; the signal light passes through the second wavelength division multiplexer (210b), a single-core fiber, a circulator (230-n), and then enters the multi-core fiber in the link to be measured. The reflected light generated in the link to be measured enters the second coupler (220b) through the circulator (230-n); the reference light is sent to the second coupler (220b); the second coupler (220b) mixes the reference light and the reflected light into a mixed-frequency signal; the mixed-frequency signal interferes in the photodetector (240) to obtain a coherent mixed-frequency signal containing the insertion loss and return loss information of the link to be measured. The photodetector (240) converts the coherent mixed-frequency signal into an electrical signal and outputs it to the data acquisition card (250), and the data acquisition card (250) converts the electrical signal into a digital signal and transmits it to the upper computer (400);

[0026] Step S3, the upper computer (400) calculates the insertion loss and return loss of each node of the link to be measured based on the digital signal.

[0027] Preferably, in step S2, the total optical intensity I total (f) of the coherent mixed-frequency signal is:

[0028] I totalI(f) = ∑I total (f i ), i ∈ [1, N]

[0029]

[0030] wherein, I total (f i ) is the total optical intensity of each core i, and N is the number of cores of the multi-core optical fiber; I ref (f i ) is the reference optical intensity of core i, and I signal (f i ) is the reflected optical intensity of core i; is the phase difference between the reference light and the reflected light.

[0031] Preferably, the host computer (400) separates the coherent mixing signal, that is, performs a Fourier transform on the total signal I total (f) received by the photodetector to convert the signal in the time domain into the frequency domain:

[0032]

[0033] wherein, I total (f) is the representation of the coherent mixing signal in the frequency domain, including the frequency components of all wavelength signals; N sharp peaks are read out according to the frequency domain diagram;

[0034] Regarding I total (f) as the superposition of N wavelength signals, separate I total (f) and extract the signal intensity of each frequency f i to obtain the signal amplitude of the frequency f i

[0035]

[0036] wherein, represents the optical intensity corresponding to the frequency f i extracted by Fourier transform;

[0037] Perform a Fourier transform again to convert the time domain into the frequency domain, and read the of each node g of core i is the optical intensity when the signal light in core i enters node g, is the optical intensity after the reflected light passes through node g, is the reflected light signal intensity reflected back from node g;

[0038] The wavelength λ i and the frequency fi Convert to the position of the corresponding optical fiber i to be measured. Let the vertical axis of the coordinate system represent the optical intensity of the corresponding wavelength, and the horizontal axis represent the position of the optical fiber to be measured. Then, the relationship between the beat signal frequency and the position is expressed as:

[0039]

[0040] In the formula, x is the position of the scattering point from the starting point node 1 of the optical fiber, f i is the frequency corresponding to the position of the scattering point, and v is the propagation speed of light in the optical fiber;

[0041] The insertion loss of the core i at the position of node g is expressed as:

[0042]

[0043] The return loss of the core i at the position of node g is expressed as:

[0044]

[0045] In the formula, is the reference optical intensity with a wavelength of λ(i);

[0046] The total insertion loss L insertion (g) of node g in the link to be measured is:

[0047]

[0048] In the formula, L insertion (p) is the total insertion loss of the fixed devices in the system, which is a preset value set according to the factory parameters; the total return loss L echo (g) of node g in the link to be measured is:

[0049]

[0050] In the formula, L echo (p) is the total return loss of the fixed devices in the system, which is a preset value set according to the factory parameters.

[0051] As can be seen from the above technical solutions, the measurement system and method for insertion loss and return loss of a multi-core optical fiber link based on OFDR provided by the embodiments of the present invention belong to the field of optical fiber link diagnosis and measurement. The system consists of a multi-wavelength laser, three wavelength division multiplexers, two couplers, N circulators, a photodetector, a data acquisition card, a link under test, and a host computer. The multi-wavelength laser outputs laser light of N wavelengths. After these signals are multiplexed by the wavelength division multiplexer, they are split into signal light and reference light by the first coupler. The signal light is output to the link under test. The mixed-frequency signal formed by the reflected light of the link under test and the reference light interferes in the photodetector, and a coherent mixed-frequency signal containing the insertion loss and return loss information of the link under test is measured. By analyzing the coherent mixed-frequency signal, the insertion loss and return loss of each node of the link under test can be calculated. Using OFDR technology, full-range measurement from the starting point to the end point of the optical fiber can be achieved, enabling OFDR to comprehensively diagnose the health status of the optical fiber link. Description of the Drawings

[0052] Figure 1 Fig. shows the structural block diagram of the measurement system for insertion loss and return loss of a multi-core optical fiber link based on OFDR provided by the embodiments of the present invention;

[0053] Figure 2 Fig. shows the structural block diagram of the link under test provided by the embodiments of the present invention;

[0054] Figure 3 Fig. shows the pattern after time-domain analysis of the interference information provided by the embodiments of the present invention;

[0055] Figure 4 Fig. shows the schematic diagram of the optical intensity and position of the optical fiber provided by the embodiments of the present invention;

[0056] Figure 5 Fig. shows the schematic diagram of the end face of the multi-core optical fiber connector provided by the embodiments of the present invention;

[0057] In the figure: multi-wavelength laser - 100, first wavelength division multiplexer - 210a, second wavelength division multiplexer - 210b, third wavelength division multiplexer - 210c, first coupler - 220a, second coupler - 220b, circulator - 230 - n, photodetector - 240, data acquisition card - 250, link under test and host computer - 400. Detailed Embodiments

[0058] The following further elaborates on the technical solutions and technical effects of the present invention in conjunction with the drawings of the present invention.

[0059] As Figure 1As shown in the figure, the present invention provides a measurement system for insertion loss and return loss of a multi-core optical fiber link based on OFDR. The system includes a multi-wavelength laser (100), a first wavelength division multiplexer (210a), a second wavelength division multiplexer (210b), a third wavelength division multiplexer (210c), a first coupler (220a), a second coupler (220b), N circulators (230-n), a photodetector (240), a data acquisition card (250), a link under test, and a host computer (400); where:

[0060] The multi-wavelength laser (100) is configured to simultaneously provide swept light of multiple wavelengths, and simultaneously provide N kinds of laser signals (f1, f2, f3... f n ) to the first wavelength division multiplexer (210a), and each frequency corresponds to a specific wavelength (λ1, λ2, λ3... λ n ).

[0061] The first wavelength division multiplexer (220a) has N input ports and 1 output port, combines the received laser signals and outputs them to the first coupler (220a); the N input ports are respectively connected to the N output ports of the multi-wavelength laser 100, and the output port of the first wavelength division multiplexer is connected to the first coupler 220a; the first wavelength division multiplexer 210a is used to multiplex optical signals of multiple different wavelengths emitted by the multi-wavelength laser 100 onto the same optical fiber for transmission.

[0062] The first coupler (220a) has 1 input port and 2 output ports, splits the received optical signal into signal light and reference light, outputs the signal light to the second wavelength division multiplexer (210b), and outputs the reference light to the second coupler (220b); the coupling ratio of the first coupler (220a) is 1:99.

[0063] The second wavelength division multiplexer (210b) has 1 input port and N output ports, and the N output ports of the second wavelength division multiplexer (210b) are respectively connected to the input ports of N circulators (230-n). The second wavelength division multiplexer (210b) is used to separate the multiplexed optical signals into multiple original optical signals of different wavelengths, and then separate the multiplexed signal light into N original signal lights of different wavelengths and output them to N circulators (230-n).

[0064] Each of the N circulators (230-n) has 3 ports, respectively outputs N original signal lights (swept light) to the link under test, and receives the reflected light of the link under test and transmits it to the third wavelength division multiplexer (210c), and the reflected light is backward Rayleigh scattering light.

[0065] The link under test is a transmission medium for optical signals, which transmits the signal light split from the first coupler 220a to various positions of the link under test, enabling it to interact with the environment under test; reference Figure 2 As shown, it consists of a multi-core fiber fan-in / fan-out device (310), A multi-core fibers (the number of cores in the multi-core fiber is N), A multi-core fiber connectors (320); N circulators (230-n) are connected to the N input ports of the multi-core fiber fan-in / fan-out device (310) through single-core fibers. A multi-core fiber connectors (320) and A multi-core fibers are alternately connected to realize the connection of multiple single-core fibers in a limited space. Among them, the first multi-core fiber at the starting position is connected to the output port of the multi-core fiber fan-in / fan-out device (310); after the N original signal lights of the N circulators (230-n) enter the multi-core fiber fan-in / fan-out device (310), N reflected lights are generated in the link under test and enter the N circulators (230-n) through the multi-core fiber fan-in / fan-out device (310); let the connection point of the A-th multi-core fiber connector (320-a) at the end of the link under test and the A-th multi-core fiber be node g, g ∈ [1, G], G = 2A, and the connection point of the first multi-core fiber and the multi-core fiber fan-in / fan-out device (310) be node 1; Rayleigh scattering occurs inside the link under test;

[0066] The third wavelength division multiplexer (210c) has N input ports and 1 output port, and is used to multiplex the multiple signal lights with different wavelengths received by the circulator 230-1, the circulator 230-2 to the circulator 230-n onto the same optical fiber for transmission, and combine and output the N received reflected lights to the second coupler (220b);

[0067] The second coupler (220b) has 2 input ports and 1 output port, mixes the reference light from the first coupler (220a) and the reflected light received from the third wavelength division multiplexer (210c) into a mixed signal and outputs it to the photodetector (240); the coupling ratio of the second coupler (220b) is 50:50;

[0068] Interference occurs in the photodetector (240) for the mixed signal to obtain a coherent mixed signal containing the insertion loss and return loss information of the link under test. The photodetector (240) converts the coherent mixed signal into an electrical signal and outputs it to the data acquisition card (250) for the data acquisition card 250 to process;

[0069] The data acquisition card (250) converts the electrical signal into a digital signal and transmits it to the host computer (400) for the host computer 400 to process;

[0070] The host computer (400) is used to receive the digital signals of the data acquisition card 250, store them as digital data, and process the acquired digital data, perform calculations according to the loss information of the link to be measured, and calculate the insertion loss and return loss of each node of the link to be measured.

[0071] The present invention provides a method for measuring the insertion loss and return loss of a multi-core optical fiber link based on the Figure 1 system shown, and the steps include:

[0072] Step S1, build a measurement system for the insertion loss and return loss of a multi-core optical fiber link based on OFDR;

[0073] Step S2, the multi-wavelength laser (100) emits optical signals f of N frequencies n , which enter the first coupler (220a) through the first wavelength division multiplexer (210a) and are divided into signal light and reference light; the signal light passes through the second wavelength division multiplexer (210b), a single-core optical fiber, a circulator (230-n), and then enters the multi-core optical fiber in the link to be measured. The reflected light generated in the link to be measured enters the second coupler (220b) through the circulator (230-n);

[0074] The reference light is sent to the second coupler (220b); the second coupler (220b) mixes the reference light and the reflected light into a mixed signal; the mixed signal interferes in the photodetector (240) to obtain a coherent mixed signal containing the insertion loss and return loss information of the link to be measured. The photodetector (240) converts the coherent mixed signal into an electrical signal and outputs it to the data acquisition card (250), and the data acquisition card (250) converts the electrical signal into a digital signal and transmits it to the host computer (400);

[0075] Step S3, the host computer (400) calculates the insertion loss and return loss of each node of the link to be measured based on the digital signals.

[0076] The reference light and the signal light returned from the link to be measured are mixed again through the coupler 220b, and the mixed signal then enters the photodetector 240 to generate interference, and the interference signal enters the data acquisition card 250; among them, the photodetector will measure the total light intensity, and this total intensity is the result of the interference between the reference light signal and the reflected light signal. The reference signal and the reflected signal are respectively R(f i ) and S(f i ), then the total light intensity I total (f) of the coherent mixed signal in step S2 is:

[0077] I total (f) = ∑I total (f i ), i ∈ [1, N] (1)

[0078]

[0079] In the formula, I total (f i ) is the total light intensity of each fiber core i, N is the number of fiber cores of the multi-core optical fiber; I ref (f i ) is the reference light intensity of fiber core i, and I signal (f i ) is the reflected light intensity of fiber core i; is the phase difference between the reference light and the reflected light, will change with the transmission characteristics, losses, etc. of the optical fiber link.

[0080] For the interference signal received by the host computer 400, signal separation is performed. The signal of each wavelength will generate periodic changes during the interference process, and its period is related to the wavelength (or frequency). The total signal is the superposition of multiple wavelength signals. These signals of different wavelengths have different frequency components in the frequency domain. Perform Fourier transform on the total signal I total (f) received by the photodetector to convert the signal in the time domain into the frequency domain. Fourier transform can decompose the composite signal into signal components of different frequencies (wavelengths):

[0081]

[0082] In the formula, I total (f) is the representation of the coherent mixing signal in the frequency domain, containing the frequency components of all wavelength signals; A total of N sharp peaks are read from the frequency domain diagram;

[0083] Regarding I total (f) as the superposition of N wavelength signals, separate I total (f) and extract the signal intensity of each frequency f i to obtain the signal amplitude of frequency f i

[0084]

[0085] In the formula, represents the light intensity corresponding to the frequency f i extracted by Fourier transform; Refer to Figure 3 the example. The total signal I total (f) is the superposition of four wavelength signals, then I total (f) is decomposed into four signals of different frequencies, and each sharp peak represents a frequency component; After separating the information, extract the intensity of each frequency component. The result of the spectrum analysis will give the intensity information of the signal of each wavelength. For each frequency f i , the amplitude of this frequency component can be obtained.

[0086] Perform the Fourier transform again to convert the time domain to the frequency domain, and read the wherein, is the optical intensity when the signal light in the fiber core i enters the node g, is the optical intensity of the reflected light after passing through the node g, is the intensity of the reflected light signal reflected back from the node g;

[0087] After obtaining the signal intensity of each wavelength through spectral analysis, convert the wavelength λ i and the frequency f i into the corresponding position of the fiber i to be measured. Referring to Figure 4 the example, let the vertical axis of the coordinate system represent the optical intensity corresponding to the wavelength, and the horizontal axis represent the position of the fiber to be measured. Then the relationship between the beat frequency signal frequency and the position is expressed as:

[0088]

[0089] In the formula, x is the position of the scattering point from the starting point node 1 of the fiber, f i is the frequency corresponding to the position of the scattering point, and v is the propagation speed of light in the fiber;

[0090] The calculation method of the loss is closely related to the intensity change of the wavelength signal; among them, the insertion loss is the signal intensity loss caused by the attenuation of the fiber link to be measured. It is usually calculated by the ratio of the input signal intensity to the output signal intensity. The insertion loss of the fiber core i at the position of the node g

[0091]

[0092] The return loss of the fiber core i at the position of the node g

[0093]

[0094] In the formula, is the reference optical intensity with the wavelength of λ(i);

[0095] The total insertion loss L insertion (g) of the node g in the link to be measured is:

[0096]

[0097] In the formula, L insertion(p) is the total insertion loss of the fixed devices in the system (the sum of the losses of each device in the system, such as circulators, couplers, wavelength division multiplexers, etc.), which is a preset value set according to the factory parameters or obtained by pre-measurement. The total insertion loss of the fixed devices can correct the insertion loss of the link to be measured;

[0098] The total return loss L of node g in the link to be measured echo (g) is:

[0099]

[0100] In the formula, L echo (p) is the total return loss of the fixed devices in the system, which is a preset value set according to the factory parameters or obtained by pre-measurement. The total return loss of the fixed devices can correct the return loss of the link to be measured.

[0101] Reference Figure 5 Referring to the cross-sectional structure of the multi-core optical fiber shown, since the number of single-core fibers required for the test link is large, the multi-core optical fiber adopted in the present invention can actually be a multi-core optical fiber assembly, which is composed of multiple multi-core optical fibers, a spiral sheath, an inner sheath, aramid, and an outer sheath from the inside to the outside in sequence.

[0102] In the calculation of the insertion loss of the link to be measured in the present invention, a correction term is adopted to eliminate the losses of other fixed devices, so as to obtain the true insertion loss value of the link. The insertion loss of the fixed devices can be kept unchanged during each measurement. Subtracting the total insertion loss of the fixed devices from the total insertion loss can obtain the insertion loss information of the link to be measured. These device insertion losses are regarded as "known" or "fixed" parameters and are carried out when calculating the insertion loss of the optical fiber to be measured, and the losses of these known devices are eliminated in data processing.

[0103] Combined with Figure 4 As shown, at the protruding regions x1, x2, and x3 in the figure, the reflections are caused by the multi-core optical fiber connector joints or discontinuities. The reflected signals are strong, indicating that the return loss is large. When the return loss is large, it will cause the stability of the light source to decrease and the dynamic range of the measurement system to be limited; when the signal passes through a certain device or optical fiber link, the light intensity is reduced due to attenuation or loss. The sunken regions Q1, Q2, and Q3 in the figure indicate that the insertion loss is large. When the insertion loss is large, the power at the receiving end is insufficient and the communication link is interrupted.

[0104] Therefore, through the solution of the present invention, the abnormal positions of the insertion loss and return loss can be quickly judged according to the calculation results of the insertion loss and return loss, and the fault location efficiency can be improved. By using the OFDR technology, the full-range measurement from the starting point to the end point of the optical fiber can be realized, so that the OFDR can comprehensively diagnose the health status of the optical fiber link, and the optical fiber can be regarded as countless distributed sensors. By analyzing the Rayleigh scattering signals, the distributed loss measurement of the optical fiber link can be realized.

[0105] The embodiments disclosed in this specification are only an illustration of the unilateral features of the present invention. The protection scope of the present invention is not limited to these embodiments, and any other functionally equivalent embodiments fall within the protection scope of the present invention. For those skilled in the art, various corresponding changes and deformations can be made according to the technical solutions and concepts described above, and all these changes and deformations should fall within the protection scope of the claims of the present invention.

Claims

1. A measurement system for insertion loss and return loss of a multi-core optical fiber link based on OFDR, characterized in that: include: A multi-wavelength laser (100), a first wavelength division multiplexer (210a), a second wavelength division multiplexer (210b), a third wavelength division multiplexer (210c), a first coupler (220a), a second coupler (220b), N circulators (230-n), a photoelectric detector (240), a data acquisition card (250), a link to be tested, and a host computer (400); The multi-wavelength laser (100) simultaneously provides laser signals of N wavelengths to the first wavelength division multiplexer (210a); The first wavelength division multiplexer (220a) has N input ports and one output port, and combines the received laser signals and outputs them to the first coupler (220a); The first coupler (220a) has one input port and two output ports, splits the received optical signal into signal light and reference light, outputs the signal light to the second wavelength division multiplexer (210b), and outputs the reference light to the second coupler (220b); The second wavelength division multiplexer (210b) has one input port and N output ports, and separates the multiplexed transmitted signal light into N original signal lights with different wavelengths and outputs them to N circulators (230-n); The N circulators (230-n) each have three ports, and respectively output the N original signal lights to the link to be tested, and receive reflected light of the link to be tested and transmit it to a third wavelength division multiplexer (210c), wherein the reflected light is backscattered Rayleigh light; The link to be tested consists of a multi-core fiber fan-in and fan-out device (310), A multi-core optical fibers, and A multi-core optical fiber connectors (320); N circulators (230-n) are connected to N input ports of the multi-core optical fiber fan-in and fan-out device (310) via single-core optical fibers, and A multi-core optical fiber connectors (320) and A multi-core optical fibers are alternately connected, wherein a first multi-core optical fiber located at an end point is connected to an output port of the multi-core optical fiber fan-in and fan-out device (310); after the N original signal lights of the N circulators (230-n) enter the multi-core optical fiber fan-in and fan-out device (310), the link to be tested generates N reflected lights which enter the N circulators (230-n) via the multi-core optical fiber fan-in and fan-out device (310); The third wavelength division multiplexer (210c) has N input ports and one output port, and combines the received N reflected light beams and outputs them to the second coupler (220b); The second coupler (220b) has two input ports and one output port, mixes the reference light from the first coupler (220a) and the reflected light received from the third wavelength division multiplexer (210c) into a mixed signal and outputs the mixed signal to the photodetector (240); The mixed signal interferes in the photodetector (240) to obtain a coherent mixed signal containing the insertion loss and return loss information of the link to be tested, and the photodetector (240) converts the coherent mixed signal into an electrical signal and outputs it to a data acquisition card (250); The data acquisition card (250) converts the electrical signal into a digital signal and transmits the digital signal to the host computer (400); The host computer (400) calculates the insertion loss and return loss of each node of the link to be tested based on the digital signal.

2. The OFDR-based multi-core optical fiber link insertion loss and return loss measurement system as claimed in claim 1, characterized in that: The multi-wavelength laser is configured to simultaneously provide swept light of multiple wavelengths.

3. The OFDR-based multi-core optical fiber link insertion loss and return loss measurement system as claimed in claim 2, characterized in that: The coupling ratio of the first coupler (220a) is 1:99, and the coupling ratio of the second coupler (220b) is 50:

50.

4. The OFDR-based multi-core optical fiber link insertion loss and return loss measurement system as claimed in claim 3, characterized in that: Let the connection point between the Ath multi-core fiber connector (320-a) and the Ath multi-core fiber located at the end of the link to be tested be node g, g∈[1,G], G=2A, and the connection point between the first multi-core fiber and the multi-core fiber fan-in and fan-out device (310) be node 1.

5. The OFDR-based multi-core optical fiber link insertion loss and return loss measurement system as claimed in claim 4, characterized in that: The total light intensity I of the coherent mixing signal total (f) is: I total (f)=∑I total (f i ),i∈[1,N] In the formula, I total (f i ) is the total light intensity of each core i, and N is the number of cores of the multi-core optical fiber; I ref (f i ) is the reference light intensity of core i, I signal (f i ) is the reflected light intensity of core i; is the phase difference between the reference light and the reflected light.

6. The OFDR-based multi-core optical fiber link insertion loss and return loss measurement system as claimed in claim 5, characterized in that: The host computer (400) performs signal separation on the coherent mixing signal, that is, the total signal I received by the photoelectric detector total (f) Perform Fourier transform to convert the time domain signal into the frequency domain: In the formula, I total (f) is a representation of the coherent mixing signal in the frequency domain, including the frequency components of all wavelength signals; a total of N sharp peaks are read out according to the frequency domain diagram; Video I total (f) is the superposition of N wavelength signals, separation I total (f) and extract each frequency f i The signal strength is obtained as f i The signal amplitude In the formula, represents the frequency f extracted by Fourier transform i The corresponding light intensity; Perform Fourier transform again to convert the time domain into frequency domain and read the core i at each node g in, is the light intensity of the signal light in core i when it enters node g, is the intensity of the reflected light after passing through node g, is the intensity of the reflected light signal reflected from node g; The wavelength λ i and frequency f i Converted to the position of the corresponding optical fiber i to be tested, let the vertical axis of the coordinate system represent the light intensity of the corresponding wavelength, and the horizontal axis represent the position of the optical fiber to be tested, then the relationship between the beat signal frequency and position is expressed as: Where x is the distance between the scattering point and the fiber starting point node 1, and f i is the frequency corresponding to the position of the scattering point, and v is the propagation speed of light in the optical fiber; Insertion loss of fiber core i at node g The expression is: Return loss of fiber core i at node g The expression is: In the formula, is the reference light intensity with wavelength λ(i); The total insertion loss L of node g in the link to be tested insertion (g) is: Where, L insertion (p) is the total insertion loss of fixed devices in the system, which is a preset value set according to factory parameters; the total return loss L of node g in the link to be tested is echo (g) is: Where, L echo (p) is the total return loss of the fixed components in the system, which is a preset value set according to factory parameters.

7. The OFDR-based multi-core optical fiber link insertion loss and return loss measurement system as claimed in claim 6, characterized in that The multi-core optical fiber is composed of a plurality of multi-core optical fibers, a spiral armor sleeve, an inner sheath, aramid fiber, and an outer sheath from the inside to the outside.

8. A method for measuring insertion loss and return loss of a multi-core optical fiber link based on OFDR, characterized in that: The implementation subject is the OFDR-based multi-core optical fiber link insertion loss and return loss measurement system as described in any one of claims 1 to 7; the steps include: Step S1, building a measurement system for insertion loss and return loss of a multi-core optical fiber link based on OFDR; Step S2, the multi-wavelength laser (100) emits optical signals f of N frequencies. n , enters the first coupler (220a) through the first wavelength division multiplexer (210a) and is divided into signal light and reference light; after the signal light passes through the second wavelength division multiplexer (210b), the single-core optical fiber, the circulator (230-n), and enters the multi-core optical fiber in the link to be tested, the reflected light generated in the link to be tested enters the second coupler (220b) through the circulator (230-n); the reference light is sent to the second coupler (220b); the second coupler (220b) mixes the reference light and the reflected light into a mixed signal; the mixed signal interferes in the photoelectric detector (240) to obtain a coherent mixed signal containing the insertion loss and return loss information of the link to be tested, the photoelectric detector (240) converts the coherent mixed signal into an electrical signal and outputs it to the data acquisition card (250), the data acquisition card (250) converts the electrical signal into a digital signal and transmits it to the host computer (400); Step S3, the host computer (400) calculates the insertion loss and return loss of each node of the link to be tested based on the digital signal.

9. The method for measuring insertion loss and return loss of a multi-core optical fiber link based on OFDR as claimed in claim 8, characterized in that: In step S2, the total light intensity I of the coherent mixing signal total (f) is: I total (f)=∑I total (f i ),i∈[1,N] In the formula, I total (f i ) is the total light intensity of each core i, and N is the number of cores of the multi-core optical fiber; I ref (f i ) is the reference light intensity of core i, I signal (f i ) is the reflected light intensity of core i; is the phase difference between the reference light and the reflected light.

10. The OFDR-based multi-core optical fiber link insertion loss and return loss measurement method according to claim 9, characterized in that: The host computer (400) performs signal separation on the coherent mixing signal, that is, the total signal I received by the photoelectric detector total (f) Perform Fourier transform to convert the time domain signal into the frequency domain: In the formula, I total (f) is a representation of the coherent mixing signal in the frequency domain, including the frequency components of all wavelength signals; a total of N sharp peaks are read out according to the frequency domain diagram; Video I total (f) is the superposition of N wavelength signals, separation I total (f) and extract each frequency f i The signal strength is obtained as f i The signal amplitude In the formula, represents the frequency f extracted by Fourier transform i The corresponding light intensity; Perform Fourier transform again to convert the time domain into frequency domain and read the core i at each node g in, is the light intensity of the signal light in core i when it enters node g, is the intensity of the reflected light after passing through node g, is the intensity of the reflected light signal reflected from node g; The wavelength λ i and frequency f i Converted to the position of the corresponding optical fiber i to be tested, let the vertical axis of the coordinate system represent the light intensity of the corresponding wavelength, and the horizontal axis represent the position of the optical fiber to be tested, then the relationship between the beat signal frequency and position is expressed as: Where x is the distance between the scattering point and the fiber starting point node 1, and f i is the frequency corresponding to the position of the scattering point, and v is the propagation speed of light in the optical fiber; Insertion loss of fiber core i at node g The expression is: Return loss of fiber core i at node g The expression is: In the formula, is the reference light intensity with wavelength λ(i); The total insertion loss L of node g in the link to be tested insertion (g) is: Where, L insertion (p) is the total insertion loss of fixed components in the system, which is a preset value set according to factory parameters; The total return loss L of node g in the link to be tested echo (g) is: Where, L echo (p) is the total return loss of the fixed components in the system, which is a preset value set according to factory parameters.

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