Dual-wavelength optical frequency domain reflectometry with doppler shift mitigation

Abstract

The application belongs to the technical field of optical fiber sensing, and particularly relates to a dual-wavelength optical frequency domain reflection device and method for Doppler frequency shift suppression. The device comprises a sweep frequency laser emission unit, a light splitting interference unit, a to-be-measured optical fiber and a data acquisition and processing unit which are connected. The sweep frequency laser emission unit is used for emitting up-sweep frequency laser and down-sweep frequency laser with different initial wavelengths. The light splitting interference unit is used for splitting the light path of the combined up-sweep frequency laser and down-sweep frequency laser into a detection path and a local path. The to-be-measured optical fiber is arranged on the detection path, the sweep frequency laser is injected into the to-be-measured optical fiber, and the generated backscattering light or reflected light signal enters the detection path to form a detection path echo signal. The output end of the light splitting interference unit is connected with the data acquisition and processing unit. The light splitting interference unit is used for performing interference processing on the detection path echo signal and the light signal of the local path, and then performing combined output to the data acquisition and processing unit for analysis and processing. The application also provides a method for dual-wavelength optical frequency domain reflection for Doppler frequency shift suppression using the above device.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical fiber sensing, and particularly relates to a dual-wavelength optical frequency domain reflectometer and method for Doppler frequency shift suppression. BACKGROUND

[0002] The optical frequency domain reflectometry (OFDR) distributed optical fiber sensing technology can be widely applied to component health monitoring, new material research and development and three-dimensional shape sensing fields due to its high sensitivity, high spatial resolution and low receiving bandwidth. Generally, the demodulation scheme used in OFDR can be divided into spectrum method and phase method. The phase demodulation method has more excellent sensing spatial resolution and higher sensitivity of optical wave phase level, and thus has been widely concerned in recent years.

[0003] Considering the continuous wave detection characteristics of OFDR, the beat frequency information of a certain position of the optical fiber runs through the whole single frequency sweeping detection period. When the optical fiber is subjected to dynamic strain occurring in the surrounding environment, the phase change caused by the strain in a single frequency sweeping period is no longer constant, but changes with time. After the frequency domain demodulation of OFDR, this phenomenon is shown as a certain Doppler frequency shift in the frequency domain of the beat frequency signal. This has a serious influence and restriction on the sensing performance in the distributed measurement process of OFDR. On the one hand, in the strain region, the Doppler frequency shift gradually accumulates with the measurement distance, although it remains constant after the strain region, but the frequency shift will continue to affect the demodulation of the subsequent spatial position; on the other hand, the amplitude and frequency of the dynamic strain both affect the size of the Doppler frequency shift. Therefore, in OFDR, the Doppler frequency shift will cause the mismatch between the spatial positions along the optical fiber in different measurement periods, which may cause crosstalk in the distributed measurement, and even cause signal demodulation error or failure.

[0004] So far, most of the existing methods are based on the spectrum demodulation scheme. The main reason is that the spectrum demodulation method analyzes and utilizes the whole spectrum, and can restore the position Doppler frequency shift and the mismatch information caused thereby through the large amount of redundant information. However, in the phase demodulation scheme, the RBS signal corresponding to each spatial resolution is processed independently, and cannot be analyzed through multiple consecutive spatial resolutions as in the spectrum demodulation. Therefore, when the Doppler frequency shift occurs, it is difficult to extract or demodulate it. Therefore, it is urgent to find a new solution to eliminate the influence of the Doppler frequency shift on the OFDR distributed measurement system based on the phase demodulation.

[0005] To solve the above problems, the application provides a dual-wavelength optical frequency domain reflectometer and method for Doppler frequency shift suppression. SUMMARY

[0006] The application aims to provide a dual-wavelength optical frequency domain reflectometer and method for Doppler frequency shift suppression to solve the above problems.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] A dual-wavelength optical frequency domain reflection device with Doppler shift suppression, comprising: a frequency-sweeping laser emission unit, a light-splitting interference unit, an optical fiber to be tested, and a data acquisition and processing unit;

[0009] The output end of the frequency sweep laser emitting unit is connected to the input end of the light splitting interference unit; the frequency sweep laser emitting unit is used to emit an upper frequency sweep laser and a lower frequency sweep laser;

[0010] The optical interferometer is used to split the optical path of the combined beam of the upper sweep laser and the lower sweep laser with different starting wavelengths into a detection path and a local oscillator path. The optical fiber to be tested is arranged on the detection path. The swept laser is injected into the optical fiber to be tested, and the backscattered light or reflected light signal generated enters the detection path to form a detection path echo signal.

[0011] The output end of the spectroscopic interference unit is connected to the data acquisition and processing unit. The spectroscopic interference unit is used to perform interference processing on the echo signal of the detection path and the optical signal of the local oscillator path, and then combine and output them to the data acquisition and processing unit for analysis and processing.

[0012] Optionally, the frequency-sweeping laser emitting unit includes:

[0013] An upper frequency sweep laser and a lower frequency sweep laser, wherein the output ends of the upper frequency sweep laser and the lower frequency sweep laser are both connected to the input end of the same beam combiner, and the output end of the beam combiner is connected to the input end of the light splitting interference unit.

[0014] Optionally, the light splitting interference unit includes:

[0015] a first optical coupling splitter, whose input end is connected to the output end of the beam combiner;

[0016] The output end of the first optical coupling spectrometer is connected to the input ends of the detection optical path interference component and the local oscillator optical path interference component respectively. The detection optical path interference component and the local oscillator optical path interference component are arranged in parallel. The detection optical path interference component forms the detection path; the local oscillator optical path interference component forms the local oscillator path.

[0017] The optical fiber to be tested is connected to the detection optical path interference component;

[0018] The output ends of the detection optical path interference component and the local oscillator optical path interference component are both connected to the input end of the second optical coupling spectrometer; the output end of the second optical coupling spectrometer is connected to the input end of the data acquisition and processing unit.

[0019] Optionally, the probe light path interference assembly comprises:

[0020] an optical circulator, a first interface of the optical circulator being connected with the output end of the first optical coupler, a second interface of the optical circulator being connected with one end of the to-be-tested optical fiber;

[0021] a polarization controller, one end of the polarization controller being connected with a third interface of the optical circulator, the other end of the polarization controller being connected with the input end of the second optical coupler;

[0022] the optical circulator is used for injecting the optical signal of the probe light path into the to-be-tested optical fiber and receiving the echo signal, and finally emitting the echo signal to the polarization controller;

[0023] the polarization controller is used for controlling the polarization state, so that the polarization state of the echo signal of the probe light path and the signal of the local oscillator light path are consistent.

[0024] Optionally, the local oscillator light path interference assembly comprises:

[0025] an acousto-optic frequency shifter, one end of the acousto-optic frequency shifter being connected with the output end of the first optical coupler, the other end of the acousto-optic frequency shifter being connected with the input end of the second optical coupler;

[0026] the acousto-optic frequency shifter is used for shifting the signal to the positive half of the frequency spectrum.

[0027] Optionally, the data acquisition and processing unit comprises:

[0028] a photodetector, one end of the photodetector being connected with the output end of the second optical coupler, the other end of the photodetector being connected with the input end of the data acquisition and processing unit.

[0029] Optionally, the light ratio of the probe light path and the local oscillator light path is 90:10 or 80:20; the light splitting ratio of the second optical coupler is 50:50.

[0030] Optionally, the to-be-tested optical fiber is a weak reflection point array optical fiber, for example, an FBG array optical fiber.

[0031] A use method of a dual-wavelength optical frequency domain reflection device for suppressing Doppler frequency shift, using the dual-wavelength optical frequency domain reflection device for suppressing Doppler frequency shift, comprising the following steps:

[0032] turning on the sweep frequency laser emission unit to emit up-sweep frequency laser and down-sweep frequency laser with different starting wavelengths;

[0033] The up-sweeping laser and the down-sweeping laser enter the light-splitting interference unit simultaneously, the light signal is split by the light-splitting interference unit to the detection path and the local oscillation path, the backscattering light or the reflection light signal generated by the to-be-measured optical fiber in the detection path forms the detection path echo signal, the light signal entering the local oscillation path forms the local oscillation path signal, the detection path echo signal and the local oscillation path signal interfere and then are combined and output to the data acquisition processing unit, and the data acquisition processing unit converts the light signal into beat frequency electric signals and analyzes and processes the beat frequency electric signals.

[0034] Optionally, the data processing method of the data acquisition processing unit comprises the following steps:

[0035] Obtaining frequency domain values;

[0036] Identifying weak reflection points at different positions of the to-be-measured optical fiber, and separating the up-sweeping beat frequency signal and the down-sweeping beat frequency signal of each weak reflection point;

[0037] Performing Fourier transform on data obtained by time domain mixing of the up-sweeping beat frequency signal and the down-sweeping beat frequency signal to obtain a difference frequency signal, and extracting a Fourier phase value of the difference frequency signal;

[0038] After time axis and adjacent weak reflection points are differentiated, a phase change value caused by strain is obtained;

[0039] A dynamic strain value is obtained by demodulation.

[0040] In use, the sweep frequency laser emission unit is turned on to emit up-sweeping laser and down-sweeping laser with different initial wavelengths; the up-sweeping laser and the down-sweeping laser enter the light-splitting interference unit simultaneously, the light signal is split by the light-splitting interference unit to the detection path and the local oscillation path, the backscattering light or the reflection light signal generated by the to-be-measured optical fiber 6 in the detection path forms the detection path echo signal, the light signal entering the local oscillation path forms the local oscillation path signal, the detection path echo signal and the local oscillation path signal interfere and then are combined and output to the data acquisition processing unit, and the data acquisition processing unit converts the light signal into beat frequency electric signals and analyzes and processes the beat frequency electric signals.

[0041] Compared with the prior art, the present application has the following advantages and technical effects:

[0042] 1. The present application can significantly suppress the Doppler frequency shift caused by the disturbance (such as dynamic strain) applied on the optical fiber in the OFDR measurement system by constructing a dual-wavelength up / down-sweeping scheme with opposite sweep slopes and different initial wavelengths, and high-fidelity distributed sensing can be realized.

[0043] 2. The present application demodulates by using the differential phase of dual wavelengths, which is equivalent to constructing a synthetic wavelength in the optical fiber, and the measurement range of the system is improved compared with a single wavelength.

[0044] 3. The application uses FBG array or other weak reflection point array optical fiber to replace single-mode optical fiber as sensing optical fiber, demodulates signals at reflection points, can realize direct extraction and difference of signals in corresponding spatial resolution in dual-wavelength OFDR measurement results, and further suppresses error caused by Doppler frequency shift. Meanwhile, the weak reflection point array has higher signal-to-noise ratio compared with ordinary single-mode optical fiber, and can also avoid interference fading problem caused by RBS coherent superposition in optical fiber. BRIEF DESCRIPTION OF DRAWINGS

[0045] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments. Obviously, the drawings described in the following only constitute some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor under the premise of the drawings.

[0046] Figure 1 It is a structural schematic diagram of the present application;

[0047] Figure 2 It is a method flowchart of the present application;

[0048] Figure 3 It is a trace diagram of 10 measurements of a certain reflection point under single-wavelength in the present application;

[0049] Figure 4 It is a trace diagram of 10 measurements of the same reflection point after mixing in the present application;

[0050] Figure 5 It is a strain demodulation result under the prior art single-wavelength technology;

[0051] Figure 6 It is a strain demodulation result under the dual-wavelength technology of the present application;

[0052] 1, the upper frequency-swept laser; 2, the lower frequency-swept laser; 3, the beam combiner; 4, the first optical coupler splitter; 5, the optical circulator; 6, the optical fiber to be measured; 7, the polarization controller; 8, the acousto-optic frequency shifter; 9, the second optical coupler splitter; 10, the photodetector; 11, the data acquisition and processor. DETAILED DESCRIPTION

[0053] The technical solutions in the embodiments of the present application will be described clearly and completely in the following by combining the drawings in the embodiments of the present application. Obviously, the described embodiments only constitute some embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0054] In order to make the above objectives, characteristics and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0055] With reference to Figures 1 to 6 The present application discloses a kind of dual-wavelength optical frequency domain reflection devices of Doppler frequency shift suppression, comprising: sweep laser emission unit, light splitting interference unit, to be measured optical fiber 6 and data acquisition processing unit;

[0056] The output end of sweep laser emission unit is connected with the input end of light splitting interference unit;Sweep laser emission unit is used to emit up-sweeping frequency laser and down-sweeping frequency laser with different starting wavelengths;

[0057] Light splitting interference unit is used to split the light path of up-sweeping frequency laser and down-sweeping frequency laser with different starting wavelengths into detection path and local path, and to-be-measured optical fiber 6 is arranged on the detection path, wherein the sweep laser is injected into the to-be-measured optical fiber 6, and the backscattering light or reflected light signal generated enters the detection path to form a detection path echo signal;

[0058] The output end of light splitting interference unit is connected with the data acquisition processing unit, and light splitting interference unit is used to combine and output the detection path echo signal and the optical signal of local path after interference processing to the data acquisition processing unit for analysis and processing.

[0059] When used, turn on sweep laser emission unit to emit up-sweeping frequency laser and down-sweeping frequency laser with different starting wavelengths;Up-sweeping frequency laser and down-sweeping frequency laser enter light splitting interference unit at the same time, and light splitting interference unit splits the optical signal into detection path and local path, the backscattering light or reflected light signal generated by the optical signal in the detection path forms a detection path echo signal, and the optical signal entering the local path forms a local path signal, and after interference of the detection path echo signal and the local path signal, the combined output is output to the data acquisition processing unit, and the data acquisition processing unit converts the optical signal into beat frequency electric signal and performs analysis and processing.

[0060] As an optional embodiment, sweep laser emission unit comprises:

[0061] Up-sweeping frequency laser 1 and down-sweeping frequency laser 2, the output end of up-sweeping frequency laser 1 and down-sweeping frequency laser 2 is connected with the input end of the same beam combiner 3, and the output end of the beam combiner 3 is connected with the input end of light splitting interference unit.

[0062] Sweep laser emission unit comprises up-sweeping frequency laser 1 and down-sweeping frequency laser 2, which are connected with beam combiner 3 respectively;Up-sweeping frequency laser 1 and down-sweeping frequency laser 2 can generate linear frequency modulation continuous light signal through direct modulation or external modulation, and beam combiner 3 can be an optical wavelength division multiplexer.

[0063] As an optional embodiment, light splitting interference unit comprises:

[0064] The first optical coupling splitter 4 is connected with the output end of the beam combiner 3;

[0065] The output end of the first optical coupling splitter 4 is connected with the input end of the probe light path interference assembly and the local oscillator light path interference assembly respectively, the probe light path interference assembly and the local oscillator light path interference assembly are arranged in parallel, the probe light path interference assembly forms a probe path; and the local oscillator light path interference assembly forms a local oscillator path.

[0066] The to-be-measured optical fiber 6 is connected with the probe light path interference assembly;

[0067] The output end of the probe light path interference assembly and the local oscillator light path interference assembly is connected with the input end of the second optical coupling splitter 9; and the output end of the second optical coupling splitter 9 is connected with the input end of the data acquisition and processing unit.

[0068] As an optional implementation, the probe light path interference assembly comprises:

[0069] The optical circulator 5 is connected with the output end of the first optical coupling splitter 4 at a first interface, and connected with one end of the to-be-measured optical fiber 6 at a second interface;

[0070] The polarization controller 7 is connected with the third interface of the optical circulator 5 at one end, and connected with the input end of the second optical coupling splitter 9 at the other end;

[0071] The optical circulator 5 is used for injecting the optical signal of the probe path into the to-be-measured optical fiber 6 and receiving the echo signal, and finally emitting to the polarization controller 7;

[0072] The polarization controller 7 is used for controlling the polarization state, so that the polarization state of the echo signal of the probe path and the signal of the local oscillator path are consistent.

[0073] As an optional implementation, the local oscillator light path interference assembly comprises:

[0074] The acousto-optic frequency shifter 8 is connected with the output end of the first optical coupling splitter 4 at one end, and connected with the input end of the second optical coupling splitter 9 at the other end;

[0075] The acousto-optic frequency shifter 8 is used for shifting the signal to the positive half spectrum.

[0076] As an optional implementation, the data acquisition and processing unit comprises:

[0077] The photodetector 10 is connected with the output end of the second optical coupling splitter 9 at one end, and connected with the input end of the data acquisition and processor 11 at the other end.

[0078] As an optional implementation, the light ratio of the detection path and the local oscillator path is 90:10 or 80:20; and the splitting ratio of the second optical coupling splitter 9 is 50:50.

[0079] As an optional implementation, the optical fiber 6 to be tested is an FBG array optical fiber.

[0080] The optical fiber 6 to be tested is an FBG array optical fiber or other weak reflection point array optical fiber.

[0081] The interference structure unit includes a first optical coupling splitter 4, an optical circulator 5, a polarization controller 7, an acousto-optic frequency shifter 8 and a second optical coupling splitter 9; the first optical coupling splitter 4 is used to split the transmitted light into a detection path and a local oscillator path, and the splitting ratio can be 90 / 10 or 80 / 20; the optical circulator 5 is used to inject the detection path optical signal into the optical fiber to be tested 6, and receive the echo signal, and finally emit it to the polarization controller 7; the polarization controller 7 is used to control the polarization state so that the polarization state of the detection path echo signal and the local oscillator path signal are consistent; the acousto-optic frequency shifter 8 is used to shift the signal to the positive half spectrum; the second optical coupling splitter 9 combines the detection path echo signal and the local oscillator path signal for interference, and the splitting ratio can be 50 / 50.

[0082] The optical fiber 6 to be tested is connected to the optical circulator 5 , and the backscattered light or reflected light signal generated by the optical fiber 6 to be tested constitutes the detection path echo signal; the optical fiber 6 to be tested is an FBG array optical fiber or other weak reflection point array optical fiber.

[0083] The photodetector 10 is used to convert the interference light signal into a beat frequency electrical signal.

[0084] The data acquisition and processor 11 is connected to the photodetector 10 and is used to analyze and process the collected beat frequency signal.

[0085] The working principle of the present invention is as follows: the upper sweep laser 1 and the lower sweep laser 2 emit frequency modulated continuous light with opposite sweep slopes, which are combined by the combiner 3 and injected into the interference structure unit. The first optical coupling splitter 4 splits the light wave and injects it into the detection path and the local oscillator path respectively. The light wave of the detection path is injected into the optical fiber 6 to be tested after passing through the optical circulator 5. The optical fiber 6 to be tested generates backward Rayleigh scattering and reflected light echo signals. After passing through the optical circulator 5, it enters the polarization controller 7. The optical fiber 6 to be tested can be an FBG array fiber or other weak reflection point array fiber. The polarization controller 7 is used to control the polarization state and match the polarization state of the detection path and the local oscillator path. The local oscillator path is connected to the acousto-optic frequency shifter 8 to shift the spectrum to the positive half axis. The echo signal of the detection path and the signal of the local oscillator path enter the second optical coupling splitter 9 for interference. After being converted into a beat frequency electrical signal by the photoelectric detector 10, it is connected to the data acquisition and processor 11 for data processing.

[0086] In the present invention, the first optical coupling splitter 4 is an 80 / 20 optical coupling splitter; the second optical coupling splitter 9 is a 50 / 50 optical coupling splitter; 80% of the first optical coupling splitter 4 is connected to the detection path, and 20% is connected to the local oscillator path.

[0087] In the present invention, the wavelengths of the up-sweep laser 1 and the down-sweep laser 2 with initial frequencies ν1 and ν2 are 1546 nm and 1554 nm respectively, and the sweep slopes of the two lasers are opposite, γ1 = -γ2.

[0088] In the present invention, the delay τ corresponding to the kth weak reflection point k At , the beat frequency signal when sweeping the two wavelengths is:

[0089] s k (t)~cos(2πγ i τ k t+2πf Shift t+2πν i τ k -πγτ k 2 ), τ k <t≤T s ,

[0090] Where, γ i and ν i are the sweep slope and initial frequency of the swept light source, i=1 or 2, representing two wavelengths, f Shift The frequency shift generated by the acousto-optic frequency shifter 8 needs to exceed the beat frequency at the farthest end of the optical fiber. When strain occurs on the optical fiber, let the dynamic strain ε at a certain moment be k The delay caused by (t) is τ k <t≤T s ,in This is the initial strain at this moment. After omitting the higher-order terms, the beat frequency signal is:

[0091]

[0092] in, is the Doppler shift caused by dynamic strain.

[0093] The sweep slopes of the up-sweep laser and the down-sweep laser are opposite, γ1 = -γ2, and the beat frequency signals during up-sweep and down-sweep are:

[0094]

[0095] in, are the Doppler frequency shifts caused by dynamic strain during the up-sweep. k,up (t) and s k,down(t) mixing the difference frequency signal after mixing to obtain:

[0096]

[0097] Since v1 and v2 are close, f in the formula D,up and f D,down are close, and after subtraction, the Doppler frequency shift is greatly suppressed, which is f D,up / (f D,up -f D,down ) times suppressed compared with single-wavelength demodulation using only the up-sweeping laser 1, and f D,down / (f D,up -f D,down ) times suppressed compared with single-wavelength demodulation using only the down-sweeping laser 2; the Fourier phase can be obtained at a frequency of 2γ1τ k . From the Fourier phase, it can be seen that, by taking the frequency difference between the two lasers as the carrier frequency of the demodulation phase, the strain demodulation range is greatly improved compared with a single optical frequency.

[0098] Based on the above conclusion, the application further provides a use method of the dual-wavelength optical frequency domain reflection device for suppressing Doppler frequency shift, using the dual-wavelength optical frequency domain reflection device for suppressing Doppler frequency shift, comprising the following steps:

[0099] Turning on the sweep laser emission unit to emit the up-sweeping laser and the down-sweeping laser;

[0100] The up-sweeping laser and the down-sweeping laser enter the light interference unit at the same time, the light signal is split into the detection path and the local oscillator path by the light interference unit, the detection path echo signal is formed by the backscattering light or the reflected light signal generated by the to-be-measured optical fiber 6 in the detection path, the local oscillator path signal is formed by the in-situ light signal in the local oscillator path, and the detection path echo signal and the local oscillator path signal are combined and output to the data acquisition and processing unit after interference, the light signal is converted into beat frequency electric signal by the data acquisition and processing unit and is analyzed and processed.

[0101] As an optional implementation, the data processing method of the data acquisition and processing unit comprises the following steps:

[0102] Obtaining frequency domain values;

[0103] Identifying weak reflection points at different positions of the to-be-measured optical fiber 6, and separating the up-sweeping beat frequency signal and the down-sweeping beat frequency signal of each weak reflection point;

[0104] Performing Fourier transform on the data obtained by time domain mixing of the up-sweeping beat frequency signal and the down-sweeping beat frequency signal to obtain a difference frequency signal, and extracting a Fourier phase value of the difference frequency signal;

[0105] After the time axis and adjacent weak reflection point difference, the phase change value caused by strain is obtained;

[0106] The dynamic strain value is obtained by demodulation.

[0107] The use process of the method is:

[0108] First, collect the time domain signal and Fourier transform it to the frequency domain;

[0109] Second, identify the weak reflection points at different positions of the optical fiber through different beat frequency frequencies, and separate the up-sweep beat frequency signal s k,up (t) and the down-sweep beat frequency signal s k,down (t) of each weak reflection point, before the delay τ k k corresponding to the kth weak reflection point, if the delay caused by dynamic strain at a certain moment is τ k <t≤T s , wherein is the initial strain at this moment, and the beat frequency signals of the up-sweep and down-sweep are respectively:

[0110]

[0111] , wherein are the Doppler shifts caused by dynamic strain during up-sweep and down-sweep respectively, f Shift is the frequency shift frequency generated by the frequency shifter, and the set frequency shift size needs to exceed the beat frequency frequency of the farthest end of the optical fiber.

[0112] Third, after mixing s k,up (t) and s k,down (t), the difference frequency signal is obtained:

[0113]

[0114] Demodulation is performed at the frequency 2γ1τ k , if only the single-wavelength demodulation using the up-sweep laser 1 is used as a comparison, it can be concluded that the amount of Doppler shift is reduced by f D,up / (f D,up -f D,down ), which is about 193 times in this embodiment, indicating that the Doppler shift is significantly suppressed; the Fourier phase The frequency difference between the two lasers is used as the carrier frequency of the demodulation phase, compared with a single optical frequency, and the strain demodulation range is also improved by about 193 times.

[0115] Fourth, after the time axis and adjacent weak reflection point difference, the phase change caused by strain is obtained

[0116] Fifth, the dynamic strain ε is obtained by demodulation.k (t).

[0117] refer to Figures 3 to 6 , to explain the effect of the present invention, Figure 3 、 Figure 4 The comparison of measurement traces between the existing single-wavelength technology and the dual-wavelength solution proposed in this invention is shown. Figure 3 The trace diagram of 10 measurements of a certain reflection point at a single wavelength shows that due to the existence of Doppler frequency shift, there is a mismatch in the spatial position between different measurement cycles, which will seriously affect the subsequent phase extraction. Figure 4 The figure shows 10 measurement traces obtained after mixing the same reflection point under the dual-wavelength scheme proposed in the present invention. It can be observed that the positions of the reflection points almost completely overlap, and the Doppler shift is significantly suppressed.

[0118] Compare the final strain demodulation results as follows Figure 5 、 Figure 6 As shown, Figure 5 For the demodulated strain under the existing single-wavelength technology, the spatial mismatch leads to serious phase extraction errors, which makes the demodulated strain distorted or even completely wrong. Figure 6 This is the strain demodulation result under the dual-wavelength solution proposed in the present invention. The suppression of Doppler shift ensures the accurate extraction of the phase at the reflection point, thereby achieving high-fidelity strain demodulation.

[0119] It can be seen that compared with the prior art, the present invention has the following advantages and technical effects:

[0120] 1. By constructing a dual-wavelength up / down sweep scheme with opposite sweep slopes and different starting wavelengths, the present invention can significantly suppress the Doppler shift caused by disturbances (such as dynamic strain) applied to the optical fiber in the OFDR measurement system, thereby realizing high-fidelity distributed sensing.

[0121] 2. The present invention utilizes the differential phase of dual wavelengths for demodulation, which is equivalent to constructing a synthetic wavelength in the optical fiber, thereby improving the measurement range of the system compared to a single wavelength.

[0122] 3. This invention uses weak-reflection-point array fibers, such as FBG arrays, as sensing fibers instead of single-mode fibers. By demodulating the signal at the reflection point, this method enables direct extraction and differentiation of signals within the corresponding spatial resolution in dual-wavelength OFDR measurements, thereby suppressing errors caused by Doppler shift. Furthermore, weak-reflection-point arrays offer a higher signal-to-noise ratio than conventional single-mode fibers and avoid the interference fading caused by RBS coherent superposition in the fiber.

[0123] In the description of the present application, it needs to be understood that the terms "longitudinal", "transverse", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings, which are only for the convenience of describing the present application, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0124] The above-described embodiments are only to describe the preferred modes of the present application, and not to limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A dual-wavelength optical frequency domain reflectometry device with Doppler shift suppression, characterized in that: include: A frequency sweep laser emission unit, a light splitting interference unit, an optical fiber to be tested (6) and a data acquisition and processing unit; The output end of the frequency sweep laser emitting unit is connected to the input end of the light splitting interference unit; the frequency sweep laser emitting unit is used to emit an upper frequency sweep laser and a lower frequency sweep laser with different starting wavelengths; The optical interference unit is used to split the optical path of the combined beam of the upper frequency sweep laser and the lower frequency sweep laser into a detection path and a local oscillator path, and the optical fiber to be tested (6) is arranged on the detection path, wherein the laser is injected into the optical fiber to be tested (6), and the generated backscattered light or reflected light signal enters the detection path to form a detection path echo signal; The output end of the optical interferometer unit is connected to the data acquisition and processing unit, and the optical interferometer unit is used to perform interference processing on the echo signal of the detection path and the optical signal of the local oscillator path, and then combine and output them to the data acquisition and processing unit for analysis and processing; The frequency sweep laser emitting unit comprises: An upper frequency sweep laser (1) and a lower frequency sweep laser (2), wherein the output ends of the upper frequency sweep laser (1) and the lower frequency sweep laser (2) are both connected to the input end of the same beam combiner (3), and the output end of the beam combiner (3) is connected to the input end of the light splitting interference unit; The light splitting interference unit includes: A first optical coupling splitter (4), the input end of which is connected to the output end of the beam combiner (3); The output end of the first optical coupling spectrometer (4) is respectively connected to the input ends of the detection light path interference component and the local oscillator light path interference component, the detection light path interference component and the local oscillator light path interference component are arranged in parallel, the detection light path interference component forms the detection path; the local oscillator light path interference component forms the local oscillator path; The optical fiber to be tested (6) is connected to the detection optical path interference component; The output ends of the detection optical path interference component and the local oscillator optical path interference component are both connected to the input end of the second optical coupling spectrometer (9); the output end of the second optical coupling spectrometer (9) is connected to the input end of the data acquisition and processing unit; The local oscillator optical path interference component includes: an acousto-optic frequency shifter (8), one end of which is connected to the output end of the first optical coupling spectrometer (4), and the other end of which is connected to the input end of the second optical coupling spectrometer (9); The acousto-optic frequency shifter (8) is used to shift the signal to the positive half spectrum.

2. The dual-wavelength optical frequency domain reflectometry device with Doppler shift suppression according to claim 1, characterized in that: The detection optical path interference component includes: An optical circulator (5), wherein a first interface of the optical circulator (5) is connected to the output end of the first optical coupling splitter (4), and a second interface of the optical circulator (5) is connected to one end of the optical fiber to be tested (6); A polarization controller (7), one end of which is connected to the third interface of the optical circulator (5), and the other end of which is connected to the input end of the second optical coupling splitter (9); The optical circulator (5) is used to inject the optical signal of the detection path into the optical fiber to be tested (6) and receive the echo signal, and finally emit it to the polarization controller (7); The polarization controller (7) is used to control the polarization state so that the polarization state of the echo signal of the detection path and the signal of the local oscillator path remain consistent.

3. The dual-wavelength optical frequency domain reflectometry device with Doppler shift suppression according to claim 1, characterized in that: The data acquisition and processing unit includes: A photoelectric detector (10) has one end connected to the output end of the second optical coupling spectrometer (9), and the other end of the photoelectric detector (10) is connected to the input end of the data acquisition and processor (11).

4. The dual-wavelength optical frequency domain reflectometry device with Doppler shift suppression according to claim 1, wherein: The optical ratio of the detection path and the local oscillator path is 90:10 or 80:20; the splitting ratio of the second optical coupling splitter (9) is 50:

50.

5. The dual-wavelength optical frequency domain reflectometry device with Doppler shift suppression according to claim 1, characterized in that: The optical fiber to be tested (6) is a reflection point array optical fiber.

6. A method for using a dual-wavelength optical frequency domain reflectometry device with Doppler shift suppression, using the dual-wavelength optical frequency domain reflectometry device with Doppler shift suppression according to any one of claims 1 to 5, characterized in that: The steps include: Turning on the frequency-sweeping laser emitting unit to emit an upper frequency-sweeping laser and a lower frequency-sweeping laser with different starting wavelengths; The upper frequency sweep laser and the lower frequency sweep laser enter the optical interference unit at the same time, and the optical interference unit divides the optical signal into the detection path and the local oscillator path. The optical signal in the detection path forms the detection path echo signal through the backscattered light or reflected light signal generated by the optical fiber (6) to be tested, and enters the local oscillator path to form the local oscillator path signal. After interference, the detection path echo signal and the local oscillator path signal are combined and output to the data acquisition and processing unit, and the data acquisition and processing unit converts the optical signal into a beat frequency electrical signal and analyzes and processes it.

7. The method for using the dual-wavelength optical frequency domain reflectometry device with Doppler shift suppression according to claim 6, wherein: The data processing method of the data acquisition and processing unit comprises the following steps: Obtain frequency domain values; Identifying weak reflection points at different positions of the optical fiber (6) to be tested, and separating the up-scanning beat frequency signal and the down-scanning beat frequency signal of each weak reflection point; Performing Fourier transform on data obtained by time-domain mixing of the upscanning beat frequency signal and the downscanning beat frequency signal to obtain a difference frequency signal, and extracting a Fourier phase value of the difference frequency signal; After differentiating the time axis and adjacent weak reflection points, the phase change value caused by strain is obtained; The dynamic strain value is obtained by demodulation.

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