High-spatial-resolution TGD-OFDR system and working method thereof

Abstract

The invention discloses a high-spatial-resolution TGD-OFDR system and a working method thereof, relates to the technical field of distributed sound wave sensing, and is used for obtaining a large sweep frequency range by using relatively low modulation cost. The high-spatial-resolution TGD-OFDR system comprises a laser, an optical fiber coupler, a semiconductor optical amplifier, a broadband acoustic optical modulator, an optical isolator, a photoelectric detector, an optical fiber circulator, a photoelectric balance detector, a data acquisition card, a computer, a radio frequency signal source, a radio frequency correction unit and the like. The frequency sweeping range of the system is flexibly realized by repeated linear modulation of the low-bandwidth broadband acousto-optic modulator, the size of the frequency sweeping range is related to repeated modulation times, the frequency sweeping range can be flexibly controlled by controlling the repeated modulation times, and the spatial resolution of the system is improved; compared with a mode of using a large-bandwidth modulator and a high-performance radio-frequency signal source, the system provided by the invention has the advantages that the performance requirements on the radio-frequency signal source and the modulator are reduced, and the system cost is low.

Description

Technical Field

[0001] The present invention relates to the technical field of distributed acoustic wave sensing, and particularly to a high-spatial-resolution TGD-OFDR system and its working method. Background Art

[0002] Distributed acoustic wave sensing (DAS) technology has unique advantages such as fast measurement speed and high detection sensitivity. Compared with traditional single-frequency short-pulse schemes, time-gated digital optical frequency domain reflectometer (TGD-OFDR), as one of the distributed acoustic wave sensing technology solutions, uses chirped long pulses of light and has the advantages of high spatial resolution and large dynamic range at the same time. The spatial resolution of the TGD-OFDR system is determined by the sweep range of the chirped long pulses of light, and the sweep range is directly proportional to the spatial resolution.

[0003] Due to the extremely high performance requirements of a large sweep range for modulation devices and radio frequency signal sources, and high-bandwidth modulators such as electro-optic modulators are affected by the carrier frequency and multi-order sidebands, increasing the modulation complexity; although single-sideband modulator devices are not affected by multi-order sidebands, the modulation cost is also relatively high.

[0004] In summary, how to achieve a large sweep range at a relatively low modulation cost to obtain a TGD-OFDR system with high spatial resolution is worthy of research. Summary of the Invention

[0005] In view of the above problems, the present invention proposes a high-spatial-resolution TGD-OFDR system and its working method to achieve obtaining a large sweep range with a relatively low modulation cost.

[0006] According to one aspect of the present invention, a high-spatial-resolution TGD-OFDR system is proposed. The system includes: a laser 1, a first optical fiber coupler 2, a semiconductor optical amplifier 3, a second optical fiber coupler 4, a broadband acousto-optic modulator 5, a third optical fiber coupler 6, an optical isolator 7, a photodetector 8, an optical fiber circulator 9, a fourth optical fiber coupler 10, a photoelectric balanced detector 11, a data acquisition card 12, a computer 13, a radio frequency signal source 14, and a radio frequency correction unit 15;

[0007] The optical signal output end of the laser 1 is connected to the optical signal input end of the first optical fiber coupler 2, and the optical signal output end of the first optical fiber coupler 2 is respectively connected to the optical signal input end of the semiconductor optical amplifier 3 and the optical signal input end of the fourth optical fiber coupler 10;

[0008] The optical signal output end of the semiconductor optical amplifier 3 is connected to the optical signal input end of the second optical fiber coupler 4. The optical signal output end of the second optical fiber coupler 4 is respectively connected to the first port 9-1 of the optical fiber circulator 9 and the optical signal input end of the broadband acousto-optic modulator 5. The optical signal output end of the broadband acousto-optic modulator 5 is connected to the optical signal input end of the third optical fiber coupler 6. The optical signal output end of the third optical fiber coupler 6 is respectively connected to the optical signal input end of the optical isolator 7 and the optical signal input end of the photodetector 8. The optical signal output end of the optical isolator 7 is connected to the optical signal input end of the second optical fiber coupler 4; the second port 9-2 of the optical fiber circulator 9 is connected to the sensing optical fiber, and the third port 9-3 of the optical fiber circulator 9 is connected to the optical signal input end of the fourth optical fiber coupler 10;

[0009] The optical signal output end of the fourth optical fiber coupler 10 is connected to the optical signal input end of the photoelectric balanced detector 11. The electrical signal output ends of the photoelectric balanced detector 11 and the photodetector 8 are respectively connected to the acquisition passband of the data acquisition card 12. The data acquisition card 12 is connected to the computer 13;

[0010] The RF output end of the RF signal source 14 is respectively connected to the RF signal input end of the semiconductor optical amplifier 3, the trigger signal input end of the data acquisition card 12, and the RF input end of the RF correction unit 15;

[0011] The amplitude correction end of the RF correction unit 15 is connected to the computer 13; the RF output end of the RF correction unit 15 is connected to the optical signal input end of the broadband acousto-optic modulator 5.

[0012] In one possible implementation, the power of the laser 1 is 10 mW, the wavelength is 1550.12 nm, and the line width is 500 Hz.

[0013] In one possible implementation, the first optical fiber coupler 2 and the third optical fiber coupler 6 are 1×2 couplers, and the splitting ratio is 90:10; the second optical fiber coupler 4 and the fourth optical fiber coupler 10 are 2×2 couplers, and the splitting ratio is 50:50.

[0014] In one possible implementation, the semiconductor optical amplifier 3 is a gain-type modulator, and its extinction ratio is 30 dB; the bandwidth of the broadband acousto-optic modulator 5 is 100 MHz, and the extinction ratio is 50 dB.

[0015] In one possible implementation, the 3 dB operating bandwidth of the photodetector 8 is 4 GHz; the 3 dB operating bandwidth of the photoelectric balanced detector 11 is 10 GHz; the sampling rate of the data acquisition card 12 is 20 GS / s, and the sampling resolution is 14 bit.

[0016] According to another aspect of the present invention, a working method of a high spatial resolution TGD-OFDR system is proposed. The working method is implemented based on the above-mentioned high spatial resolution TGD-OFDR system, and the working method includes:

[0017] The continuous light output by the laser 1 is divided into two paths, the upper path and the lower path, by the first fiber coupler 2. The upper path is used as the probe light, and the lower path is used as the reference light. The continuous light on the upper path is modulated by the semiconductor optical amplifier 3 controlled by the radio frequency signal source 14. After the pulsed light is output, it is divided into two parts by the second fiber coupler 4. The first part of the pulsed light is injected into the sensing fiber through the fiber optic circulator 9. The second part of the pulsed light enters the path composed of the second fiber coupler 4, the broadband acousto-optic modulator 5, the third fiber coupler 6 and the optical isolator 7 for cyclic transmission and beam splitting. The pulsed light after cyclic transmission and beam splitting is also partly injected into the sensing fiber through the fiber optic circulator 9, and the other part continues cyclic transmission and beam splitting.

[0018] The backward Rayleigh scattering optical signal in the sensing fiber and the lower path reference light are injected into the fourth fiber coupler 10 together through the fiber optic circulator 9 for coherent beat frequency. The beat frequency result is photoelectrically converted by the photoelectric balanced detector 11, recorded by the data acquisition card 12, and transmitted to the computer 13 for data processing.

[0019] The computer 13 compresses the collected linear sweep beat frequency result into a single frequency signal by pulse compression.

[0020] In one possible implementation, during each cyclic transmission and beam splitting process, the pulsed light is linearly swept and modulated by the broadband acousto-optic modulator 5. The frequency range of the pulsed light expands exponentially with the cyclic times based on the linear sweep range of the broadband acousto-optic modulator 5. The linearly swept and modulated pulsed light passes through the third fiber coupler 6. One part of the pulsed light continues cyclic transmission through the optical isolator 7 and the second fiber coupler 4, and the other part of the pulsed light is photoelectrically converted by the photodetector 8, recorded by the data acquisition card 12, and then transmitted to the computer 13 for processing. The pulsed light complementary envelope information obtained after the computer 13 processes it is feedback-transmitted to the radio frequency correction unit 15. The radio frequency correction unit 15 corrects the radio frequency pulse shape input by the radio frequency signal source 14 based on the complementary envelope information, and uses the corrected radio frequency pulse to control the broadband acousto-optic modulator 5 for equal-amplitude linear frequency modulation.

[0021] In one possible implementation, the modulation of the continuous light on the upper path by the semiconductor optical amplifier 3 controlled by the radio frequency signal source 14 includes:

[0022] The expression of the continuous light output by the laser 1 is defined as follows:

[0023]

[0024] Among them, A c , ω c and are respectively the amplitude, frequency and initial phase of the continuous light output by the laser 1; t represents time;

[0025] The radio frequency signal source 14 outputs a radio frequency pulse signal with a width of T P , and a period of T to drive the semiconductor optical amplifier 3 to modulate the continuous light E c (t) into pulsed light E P (t). Then the time-domain representation of E P (t) is:

[0026]

[0027] Among them, W represents the window function, and A P is the amplitude of E P (t);

[0028] The repetition period of the pulsed light E P (t) is T, which depends on the length L of the sensing optical fiber: T ≥ 2nL / c, where c is the light wave propagation speed in vacuum and n is the refractive index of the sensing optical fiber.

[0029] In one possible implementation, the radio frequency correction unit 15 uses a corrected radio frequency pulse to control the broadband acousto-optic modulator 5 for equal-amplitude linear frequency modulation, including:

[0030] Define the starting modulation frequency of the broadband acousto-optic modulator 5 as f1 and the 3dB modulation bandwidth as ΔF; the radio frequency sweep signal m sweep (t) loaded by the radio frequency correction unit 15 for linear frequency sweeping on the broadband acousto-optic modulator 5 has the following time-domain expression:

[0031]

[0032] Among them, A srf is the amplitude of m sweep (t); then the chirped pulsed light E sweep (t) after the broadband acousto-optic modulator 5 performs equal-amplitude linear frequency modulation is expressed as:

[0033]

[0034] Among them, i is the number of times the broadband acousto-optic modulator 5 repeats linear modulation; Δt is the time interval of repeated modulation; A sweep is the amplitude of E sweep (t).

[0035] In one possible implementation, the computer 13 compresses the collected linear frequency sweep beat frequency result into a single-frequency signal, including:

[0036] The time-domain expression of the backward Rayleigh scattering optical signal in the sensing optical fiber is the convolution of the impulse response of the sensing optical fiber and the equivalent RF drive signal of the broadband acousto-optic modulator 5 that repetitively linearly modulates a chirped pulse light with a large sweep range; taking the anti-fold conjugate signal of the equivalent RF drive signal as a matched filter, performing convolution operations on the impulse response of the sensing optical fiber, the equivalent RF drive signal, and the anti-fold conjugate signal of the equivalent RF drive signal to obtain a single-frequency signal after pulse compression.

[0037] The beneficial technical effects of the present invention are as follows:

[0038] The present invention proposes a high spatial resolution TGD-OFDR system and its working method, having the following advantages:

[0039] 1) Flexible control of the sweep range and high spatial resolution: The sweep range of the system is flexibly realized by the repetitive linear modulation of a broadband acousto-optic modulator with low bandwidth. The size of the sweep range is related to the number of repetitive modulations, and the sweep range can be flexibly controlled by controlling the number of repetitive modulations; the sweep range determines the spatial resolution of the system, so the TGD-OFDR system of the present invention has a high spatial resolution.

[0040] 2) Low system cost: The system flexibly realizes large-range linear sweep modulation through the repetitive linear modulation of a broadband acousto-optic modulator with a low bandwidth of several tens of megahertz / hundreds of megahertz. Compared with the method of using a large-bandwidth modulator and a high-performance RF signal source, the performance requirements for the RF signal source and the modulator are reduced, so the system cost is low. Description of the Drawings

[0041] By reading the following detailed description with reference to the accompanying drawings, the above and other objects, features, and advantages of the exemplary embodiments of the present invention will become readily understood. In the drawings, several embodiments of the present invention are shown in an exemplary rather than restrictive manner, where:

[0042] Figure 1 is a schematic structural diagram of a high spatial resolution TGD-OFDR system according to an embodiment of the present invention;

[0043] Figure 2 is a time-frequency example diagram of a 2 GHz sweep range of repetitive modulation of a broadband acousto-optic modulator in an embodiment of the present invention. Detailed Embodiments

[0044] The principles and spirit of the present invention will be described below with reference to several exemplary embodiments. It should be understood that these embodiments are given only to enable those skilled in the art to better understand and then implement the present invention, and do not limit the scope of the present invention in any way. On the contrary, these embodiments are provided to make the present disclosure more thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art.

[0045] An embodiment of the present invention provides a high-spatial-resolution TGD-OFDR system. Referring to the attached Figure 1 , the system includes a laser 1, a first optical fiber coupler 2, a semiconductor optical amplifier 3, a second optical fiber coupler 4, a broadband acousto-optic modulator 5, a third optical fiber coupler 6, an optical isolator 7, a photodetector 8, an optical fiber circulator 9, a fourth optical fiber coupler 10, a photoelectric balanced detector 11, a data acquisition card 12, a computer 13, a radio frequency signal source 14, and a radio frequency correction unit 15;

[0046] The optical signal output end of the laser 1 is connected to the optical signal input end of the first optical fiber coupler 2, and the optical signal output end of the first optical fiber coupler 2 is respectively connected to the optical signal input end of the semiconductor optical amplifier 3 and the optical signal input end of the fourth optical fiber coupler 10;

[0047] The optical signal output end of the semiconductor optical amplifier 3 is connected to the optical signal input end of the second optical fiber coupler 4. The optical signal output end of the second optical fiber coupler 4 is respectively connected to the first port 9-1 of the fiber optic circulator 9 and the optical signal input end of the broadband acousto-optic modulator 5. The optical signal output end of the broadband acousto-optic modulator 5 is connected to the optical signal input end of the third optical fiber coupler 6. The optical signal output end of the third optical fiber coupler 6 is respectively connected to the optical signal input end of the optical isolator 7 and the optical signal input end of the photodetector 8. The optical signal output end of the optical isolator 7 is connected to the optical signal input end of the second optical fiber coupler 4. The second port 9-2 of the fiber optic circulator 9 is connected to the sensing optical fiber, and the third port 9-3 of the fiber optic circulator 9 is connected to the optical signal input end of the fourth optical fiber coupler 10;

[0048] The optical signal output end of the fourth optical fiber coupler 10 is connected to the optical signal input end of the photoelectric balanced detector 11. The electrical signal output ends of the photodetector 8 and the photoelectric balanced detector 11 are respectively connected to the acquisition passband of the data acquisition card 12, and the data acquisition card 12 is connected to the computer 13; The radio frequency output end of the radio frequency signal source 14 is respectively connected to the radio frequency signal input end of the semiconductor optical amplifier 3, the trigger signal input end of the data acquisition card 11, and the radio frequency input end of the radio frequency correction unit 15, and the computer 13 is connected to the amplitude correction end of the radio frequency correction unit 15; The radio frequency output end of the radio frequency correction unit 15 is connected to the optical signal input end of the broadband acousto-optic modulator 5.

[0049] In this embodiment, preferably, the power of the laser 1 is 10 mW, the wavelength is 1550.12 nm, and the line width is 500 Hz.

[0050] In this embodiment, preferably, the first optical fiber coupler 2 and the third optical fiber coupler 6 are 1×2 couplers, and the splitting ratio is 90:10; the second optical fiber coupler 4 and the fourth optical fiber coupler 10 are 2×2 couplers, and the splitting ratio is 50:50.

[0051] In this embodiment, preferably, the semiconductor optical amplifier 3 is a gain modulator, and its extinction ratio is 30 dB; the broadband acousto-optic modulator 5 has a bandwidth of 100 MHz and an extinction ratio of 50 dB.

[0052] In this embodiment, preferably, the 3 dB operating bandwidth of the photodetector 8 is 4 GHz, and the 3 dB operating bandwidth of the photoelectric balanced detector 11 is 10 GHz.

[0053] In this embodiment, preferably, the sampling rate of the data acquisition card 12 is 20 GS / s, and the sampling resolution is 14 bits.

[0054] Another embodiment of the present invention provides a working method for a high spatial resolution TGD-OFDR system, and the working method is implemented based on the high spatial resolution TGD-OFDR system described in the above embodiment; the working method includes:

[0055] The continuous light output by the laser 1 is divided into two paths, the upper path is used as the detection light, and the lower path is used as the reference light; the continuous light on the upper path is modulated by the semiconductor optical amplifier 3 controlled by the radio frequency signal source 13, and after the pulsed light is output, it is divided into two parts by the second optical fiber coupler 4. The first part of the pulsed light is injected into the sensing optical fiber through the optical fiber circulator 9; the second part of the pulsed light enters the path composed of the second optical fiber coupler 4, the broadband acousto-optic modulator 5, the third optical fiber coupler 6 and the optical isolator 7 for circular transmission and beam splitting, so as to realize the flexible and controllable expansion of the sweep range; the pulsed light after circular transmission and beam splitting is also partly injected into the sensing optical fiber through the optical fiber circulator 9, and the other part continues circular transmission and beam splitting;

[0056] In each cycle of transmission, the pulsed optical signal is linearly frequency-swept modulated by the broadband acousto-optic modulator 5. The frequency range of the pulsed light expands multiplicatively with the cycle number, with the linear frequency-sweeping range of the broadband acousto-optic modulator 5 as the base. The linearly frequency-swept modulated pulsed light passes through the third fiber coupler 6. A part of the pulsed light continues to circulate through the optical isolator 7 and the second fiber coupler 4, while the other part is photoelectrically converted by the photodetector 8 and recorded by the data acquisition card 12 and then transmitted to the computer 13 for processing. Since the phase (frequency) information of the pulsed light is much larger than the response bandwidth of the photodetector 8, the detected data is the envelope amplitude information of the pulsed light and does not contain the pulsed light phase information. Based on the envelope information of the pulsed light, the complementary envelope information of the pulsed light is solved in real time and fed back to the radio frequency correction unit 15. The radio frequency correction unit 15 corrects the radio frequency pulse shape input by the radio frequency signal source 14 based on the complementary envelope information of the pulsed light fed back by the computer 13. The corrected radio frequency pulse then controls the broadband acousto-optic modulator 5 to perform equal-amplitude linear frequency modulation, effectively avoiding the amplitude nonlinear response generated when the broadband acousto-optic modulator 5 performs linear frequency modulation on the pulsed light;

[0057] The backward Rayleigh scattering optical signal in the sensing optical fiber and the dropped reference light are injected into the fourth fiber coupler 10 through the fiber optic circulator 9 for coherent beat frequency. The beat frequency result is photoelectrically converted by the photoelectric balanced detector 11, recorded by the data acquisition card 12, and transmitted to the computer 13 for data processing; the computer 13 compresses the collected linearly frequency-swept beat frequency result into a single-frequency signal.

[0058] At this time, the spatial resolution of the system depends on the linear frequency-sweeping range, and the frequency-sweeping range of this system is flexibly realized by repeated modulation of the low-bandwidth acousto-optic modulator. Attached Figure 2 is the time-frequency diagram of the frequency-sweeping range of the repeated linear frequency-sweeping modulation of the broadband acousto-optic modulator. It can be seen that the system expands the frequency-sweeping range to 2 GHz at a relatively low cost.

[0059] In this embodiment, preferably, the process of modulating the pulsed light by the semiconductor optical amplifier 3 is as follows:

[0060] First, define the expression of the continuous light output by the wide laser 1 as follows:

[0061]

[0062] where A c 、ω c and are the amplitude, frequency, and initial phase of the continuous light output by the laser 1 respectively

[0063] The radio frequency signal source 12 outputs a radio frequency pulse signal with a width of T P , a period of T to drive the semiconductor optical amplifier 3 to convert the continuous light Ec (t) is modulated into pulsed light E P (t), and the time-domain representation of E P (t) is

[0064]

[0065] where W represents the window function and A P is the amplitude of E P (t).

[0066] While modulating the continuous light into pulsed light, the semiconductor optical amplifier 3 amplifies the optical signal, and it is a gain-type modulator. The repetition period T of the pulsed light E P (t) depends on the length L of the sensing optical fiber and should satisfy T≥2nL / c, where c is the light wave propagation speed in vacuum and n is the refractive index of the sensing optical fiber.

[0067] In this embodiment, preferably, the process of the radio frequency correction unit 15 using the corrected radio frequency pulse to control the broadband acousto-optic modulator 5 for equal-amplitude linear frequency modulation is as follows:

[0068] Define the starting modulation frequency of the broadband acousto-optic modulator 5 as f1 and the 3dB modulation bandwidth as ΔF; the radio frequency sweep signal m sweep (t) loaded by the radio frequency correction unit 15 for linear frequency sweeping on the broadband acousto-optic modulator 5 has the following time-domain expression:

[0069]

[0070] where A srf is the amplitude of m sweep (t).

[0071] The chirped pulsed light E sweep (t) modulated by the broadband acousto-optic modulator 5 has the following time-domain expression:

[0072]

[0073] where i is the number of times of repeated linear modulation of the broadband acousto-optic modulator 5; A sweep is the amplitude of E sweep (t); Δt is the time interval of repeated modulation. The sweep range of the chirped pulsed light depends on the bandwidth ΔF and the modulation times i of the broadband acousto-optic modulator 5. Avoid using high-bandwidth, high-performance modulators and radio frequency signal source signals, as well as sideband crosstalk; realize flexible control of the sweep range at a lower cost.

[0074] In this embodiment, preferably, the process by which the computer 13 compresses the collected linear swept-frequency beat frequency result into a single-frequency signal is as follows: The time-domain expression of the backward Rayleigh scattering optical signal in the sensing optical fiber is the convolution of the impulse response of the sensing optical fiber and the equivalent radio-frequency drive signal of the broadband acousto-optic modulator 5 that repeatedly linearly modulates a chirped pulse light with a large swept-frequency range; taking the anti-fold conjugate signal of the equivalent radio-frequency drive signal as the matching filter, performing a convolution operation on the impulse response of the sensing optical fiber, the equivalent radio-frequency drive signal, and the anti-fold conjugate signal of the equivalent radio-frequency drive signal to obtain the single-frequency signal after pulse compression.

[0075] Specifically, the time-domain signal of the backward Rayleigh scattering optical signal in the optical fiber can be expressed as follows:

[0076]

[0077] where τ is the time delay; is the convolution operation; h(t) is the impulse response of the sensing optical fiber, h(t) = A(t)cos(-ω c t); s(t) is the equivalent radio-frequency drive signal of the broadband acousto-optic modulator 5 that repeatedly linearly modulates a chirped pulse light with a large swept-frequency range. At this time, T P determines the system spatial resolution, and the resolution is relatively low. During data processing, the anti-fold conjugate signal s * (-t) of s(t) is generated in the digital domain as the matching filter, and E RBS (t) is compressed as follows:

[0078]

[0079] After compression is equivalent to a new sinc function-shaped narrow pulse. At this time, the system spatial resolution is the full width at half maximum (FWHM) of the main lobe of the system sinc function-shaped narrow pulse, that is, the swept-frequency range iΔF of the chirped pulse light. The spatial resolution is expressed as follows:

[0080]

[0081] It can be seen that the spatial resolution of the system of the present invention depends on the swept-frequency range iΔF of the chirped pulse light, avoiding the use of high-bandwidth and high-performance modulators and radio-frequency signal source signals, as well as sideband crosstalk; realizing flexible control of the swept-frequency range at a relatively low cost and achieving high spatial resolution.

[0082] A high-spatial-resolution TGD-OFDR system and its working method proposed by the present invention have the following advantages: 1) Flexible control of the frequency-sweeping range and high spatial resolution: The frequency-sweeping range of the system is flexibly realized by the repeated linear modulation of an acousto-optic modulator with low bandwidth. The size of the frequency-sweeping range is related to the number of repeated modulations, and the frequency-sweeping range can be flexibly controlled by controlling the number of repeated modulations; the frequency-sweeping range determines the spatial resolution of the system, so the TGD-OFDR system of the present invention has a high spatial resolution. 2) Low system cost: The system flexibly realizes a large-range linear frequency-sweeping modulation through the repeated linear modulation of an acousto-optic modulator with a low bandwidth of dozens of megahertz / hundreds of megahertz. Compared with the method of using a large-bandwidth modulator and a high-performance radio frequency signal source, the performance requirements for the radio frequency signal source and the modulator are reduced, and the system cost is low.

[0083] Although the spirit and principles of the present invention have been described with reference to several specific embodiments, it should be understood that the present invention is not limited to the specific embodiments disclosed, and the division of each aspect does not mean that the features in these aspects cannot be combined for benefits. This division is only for the convenience of expression. The present invention aims to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A high spatial resolution TGD-OFDR system, characterized in that: include: Laser (1), first optical fiber coupler (2), semiconductor optical amplifier (3), second optical fiber coupler (4), broadband acousto-optic modulator (5), third optical fiber coupler (6), optical isolator (7), photoelectric detector (8), optical fiber circulator (9), fourth optical fiber coupler (10), photoelectric balanced detector (11), data acquisition card (12), computer (13), radio frequency signal source (14), radio frequency correction unit (15); The optical signal output end of the laser (1) is connected to the optical signal input end of the first optical fiber coupler (2), and the optical signal output end of the first optical fiber coupler (2) is respectively connected to the optical signal input end of the semiconductor optical amplifier (3) and the optical signal input end of the fourth optical fiber coupler (10); The optical signal output end of the semiconductor optical amplifier (3) is connected to the optical signal input end of the second optical fiber coupler (4); the optical signal output end of the second optical fiber coupler (4) is respectively connected to the first port (9-1) of the optical fiber circulator (9) and the optical signal input end of the broadband acousto-optic modulator (5); the optical signal output end of the broadband acousto-optic modulator (5) is connected to the optical signal input end of the third optical fiber coupler (6); the optical signal output end of the third optical fiber coupler (6) is respectively connected to the optical signal input end of the optical isolator (7) and the optical signal input end of the photodetector (8); the optical signal output end of the optical isolator (7) is connected to the optical signal input end of the second optical fiber coupler (4); the second port (9-2) of the optical fiber circulator (9) is connected to the sensing optical fiber; the third port (9-3) of the optical fiber circulator (9) is connected to the optical signal input end of the fourth optical fiber coupler (10); The optical signal output end of the fourth optical fiber coupler (10) is connected to the optical signal input end of the photoelectric balance detector (11), the electrical signal output end of the photoelectric balance detector (11) and the electrical signal output end of the photoelectric detector (8) are respectively connected to the acquisition passband of the data acquisition card (12), and the data acquisition card (12) is connected to the computer (13); The radio frequency output end of the radio frequency signal source (14) is respectively connected to the radio frequency signal input end of the semiconductor optical amplifier (3), the trigger signal input end of the data acquisition card (12), and the radio frequency input end of the radio frequency correction unit (15); The amplitude correction end of the radio frequency correction unit (15) is connected to the computer (13); the radio frequency output end of the radio frequency correction unit (15) is connected to the optical signal input end of the broadband acousto-optic modulator (5).

2. A high spatial resolution TGD-OFDR system according to claim 1, characterized in that: The power of the laser (1) is 10 mW, the wavelength is 1550.12 nm, and the line width is 500 Hz.

3. A high spatial resolution TGD-OFDR system according to claim 1, characterized in that: The first optical fiber coupler (2) and the third optical fiber coupler (6) are 1×2 couplers with a splitting ratio of 90:10; the second optical fiber coupler (4) and the fourth optical fiber coupler (10) are 2×2 couplers with a splitting ratio of 50:

50.

4. A high spatial resolution TGD-OFDR system according to claim 1, characterized in that: The extinction ratio of the semiconductor optical amplifier (3) is 30 dB; the bandwidth of the broadband acousto-optic modulator (5) is 100 MHz, and the extinction ratio is 50 dB.

5. A high spatial resolution TGD-OFDR system according to claim 1, characterized in that: The 3dB working bandwidth of the photoelectric detector (8) is 4 GHz; the 3dB working bandwidth of the photoelectric balance detector (11) is 10 GHz; the sampling rate of the data acquisition card (12) is 20 GS / s, and the sampling resolution is 14 bits.

6. A method for operating a high spatial resolution TGD-OFDR system, characterized in that: The working method is implemented based on the high spatial resolution TGD-OFDR system according to any one of claims 1 to 5, and the working method comprises: The continuous light output by the laser (1) is divided into two paths, an upper path and an lower path, through a first optical fiber coupler (2), wherein the upper path is used as detection light and the lower path is used as reference light; the upper path continuous light is modulated by a semiconductor optical amplifier (3) controlled by a radio frequency signal source (14), and after outputting pulse light, it is divided into two parts through a second optical fiber coupler (4); the first part of the pulse light is injected into the sensing optical fiber through an optical fiber circulator (9); the second part of the pulse light enters a path composed of the second optical fiber coupler (4), a broadband acousto-optic modulator (5), a third optical fiber coupler (6) and an optical isolator (7) for cyclic transmission and beam splitting; a part of the pulse light after cyclic transmission and beam splitting is also injected into the sensing optical fiber through the optical fiber circulator (9), and the other part continues to be cyclically transmitted and beam splitted; The backscattered Rayleigh light signal in the sensing optical fiber is injected into the fourth optical fiber coupler (10) together with the downlink reference light through the optical fiber circulator (9) for coherent frequency beat, and the frequency beat result is photoelectrically converted by the photoelectric balance detector (11), recorded by the data acquisition card (12), and transmitted to the computer (13) for data processing; The computer (13) compresses the collected linear frequency sweep and beat frequency results into a single frequency signal through pulse compression.

7. A high spatial resolution TGD-OFDR working method according to claim 6, characterized in that: In each cyclic transmission and beam splitting process, the pulse light is linearly swept modulated by the broadband acousto-optic modulator (5), and the frequency range of the pulse light is multiplied with the number of cycles based on the linear sweep range of the broadband acousto-optic modulator (5); the pulse light after linear sweep modulation passes through the third optical fiber coupler (6), a part of the pulse light passes through the optical isolator (7) and the second optical fiber coupler (4) and continues to be cyclically transmitted, and the other part of the pulse light is photoelectrically converted by the photoelectric detector (8), recorded by the data acquisition card (12) and transmitted to the computer (13) for processing; the complementary envelope information of the pulse light obtained after processing by the computer (13) is fed back and transmitted to the radio frequency correction unit (15), and the radio frequency correction unit (15) corrects the radio frequency pulse shape input by the radio frequency signal source (14) based on the complementary envelope information, and uses the corrected radio frequency pulse to control the broadband acousto-optic modulator (5) to perform equal amplitude linear frequency modulation.

8. A high spatial resolution TGD-OFDR working method according to claim 7, characterized in that: The added continuous light is modulated by a semiconductor optical amplifier (3) controlled by a radio frequency signal source (14), and includes: The expression for defining the continuous light output by the laser (1) is as follows: Among them, A c ,ω c and are the amplitude, frequency and initial phase of the continuous light output by the laser (1), respectively; t represents the time; The output width of the RF signal source (14) is T P The radio frequency pulse signal with a period of T drives the semiconductor optical amplifier (3) to convert the continuous light E c (t) modulated into pulse light E P (t), then E P The time domain representation of (t) is: Where W represents the window function, A P For E P The amplitude of (t); Pulse Light E P The repetition period of (t) is T, which depends on the length L of the sensing fiber: T ≥ 2nL / c, where c is the propagation speed of light waves in vacuum and n is the refractive index of the sensing fiber.

9. A high spatial resolution TGD-OFDR working method according to claim 8, characterized in that: The radio frequency correction unit (15) uses the corrected radio frequency pulse to control the broadband acousto-optic modulator (5) to perform equal amplitude linear frequency modulation, including: The starting modulation frequency of the broadband acousto-optic modulator (5) is defined as f1, and the 3dB modulation bandwidth is defined as ΔF; the radio frequency correction unit (15) is loaded on the broadband acousto-optic modulator (5) to generate a radio frequency sweep signal m for performing linear frequency sweeping. sweep The time domain expression of (t) is as follows: Among them, A srf is m sweep The amplitude of (t); the chirped pulse light E after the broadband acousto-optic modulator (5) performs equal amplitude linear frequency modulation sweep The expression of (t) is: Wherein, i is the number of times the broadband acousto-optic modulator (5) repeats linear modulation; Δt is the time interval of repeated modulation; A sweep For E sweep (t) amplitude.

10. A high spatial resolution TGD-OFDR working method according to claim 9, characterized in that: The computer (13) compresses the collected linear frequency sweep beat frequency results into a single frequency signal through pulse compression, including: The time domain expression of the backscattered Rayleigh light signal in the sensing optical fiber is the convolution of the impulse response of the sensing optical fiber and the equivalent radio frequency driving signal of the chirped pulse light with a large frequency sweep range repeatedly linearly modulated by a broadband acousto-optic modulator (5); the anti-convolution conjugate signal of the equivalent radio frequency driving signal is used as a matching filter, and the impulse response of the sensing optical fiber, the equivalent radio frequency driving signal, and the anti-convolution conjugate signal of the equivalent radio frequency driving signal are convolved to obtain a single-frequency signal after pulse compression.

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