TGD-OFDR system for expanding sweep frequency range based on broadband acousto-optic modulation

Abstract

The utility model discloses a TGD-OFDR system for expanding a sweep frequency range based on broadband acousto-optic modulation, 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 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 TGD-OFDR system provided by the utility model 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; and compared with a mode of using a large-bandwidth modulator and a high-performance radio frequency signal source, the performance requirements on the radio frequency signal source and the modulator are reduced, and the system cost is low.

Description

Technical Field

[0001] This utility model relates to the field of distributed acoustic wave sensing technology, specifically to a TGD-OFDR system based on broadband acousto-optic modulation to extend the sweep frequency range. Background Technology

[0002] Distributed acoustic sensing (DAS) technology boasts unique advantages such as high measurement speed and high detection sensitivity. Compared to traditional single-frequency short-pulse schemes, the Time-Gated Digital Optical Frequency Domain Reflectometer (TGD-OFDR), as one of the distributed acoustic sensing technologies, utilizes chirped long-pulse light and simultaneously offers the advantages of high spatial resolution and a large dynamic range. The spatial resolution of the TGD-OFDR system is determined by the frequency sweep range of the chirped long-pulse light, and the frequency sweep range is directly proportional to the spatial resolution.

[0003] Because a large sweep frequency range places extremely high demands on the performance of 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, their modulation cost is also relatively high.

[0004] In summary, it is worthwhile to study how to achieve a large frequency sweep range with low modulation cost in order to obtain a TGD-OFDR system with high spatial resolution. Utility Model Content

[0005] In view of the above problems, this utility model proposes a TGD-OFDR system based on broadband acousto-optic modulation to extend the sweep frequency range, so as to achieve a large sweep frequency range with low modulation cost.

[0006] A TGD-OFDR system based on broadband acousto-optic modulation to extend the frequency sweep range includes: a laser 1, a first fiber coupler 2, a semiconductor optical amplifier 3, a second fiber coupler 4, a broadband acousto-optic modulator 5, a third fiber coupler 6, an optical isolator 7, a photodetector 8, a fiber optic circulator 9, a fourth 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 terminal of laser 1 is connected to the optical signal input terminal of the first fiber coupler 2, and the optical signal output terminal of the first fiber coupler 2 is connected to the optical signal input terminal of semiconductor optical amplifier 3 and the optical signal input terminal of the fourth fiber coupler 10 respectively.

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

[0009] The optical signal output terminal of the fourth fiber optic coupler 10 is connected to the optical signal input terminal of the photoelectric balance detector 11. The electrical signal output terminals of the photoelectric balance detector 11 and the photoelectric detector 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 radio frequency output terminal of the radio frequency signal source 14 is connected to the radio frequency signal input terminal of the semiconductor optical amplifier 3, the trigger signal input terminal of the data acquisition card 12, and the radio frequency input terminal of the radio frequency correction unit 15, respectively.

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

[0012] In one possible implementation, the laser 1 has a power of 10mW, a wavelength of 1550.12nm, and a linewidth of 500Hz.

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

[0014] In one possible implementation, the semiconductor optical amplifier 3 is a gain modulator with an extinction ratio of 30dB.

[0015] In one possible implementation, the broadband acousto-optic modulator 5 has a bandwidth of 100 MHz and an extinction ratio of 50 dB.

[0016] In one possible implementation, the photodetector 8 has a 3dB operating bandwidth of 4 GHz.

[0017] In one possible implementation, the photoelectric balance detector 11 has a 3dB operating bandwidth of 10 GHz.

[0018] In one possible implementation, the data acquisition card 12 has a sampling rate of 20 GS / s and a sampling resolution of 14 bits.

[0019] The beneficial technical effects of this utility model are:

[0020] This invention proposes a TGD-OFDR system based on broadband acousto-optic modulation to extend the frequency sweep range, which has the following advantages:

[0021] 1) Flexible control of sweep range and high spatial resolution: The sweep range of the system is flexibly achieved by repetitive linear modulation of a low-bandwidth broadband acousto-optic modulator. The size of the sweep range is related to the number of repetitions, and the sweep range can be flexibly controlled by controlling the number of repetitions. The sweep range determines the spatial resolution of the system, so the system has high spatial resolution.

[0022] 2) Low system cost: The system uses a broadband acousto-optic modulator with a low bandwidth of tens or hundreds of megahertz to flexibly achieve large-range linear sweep frequency modulation. Compared with the method of using a large bandwidth modulator and a high-performance radio frequency signal source, the performance requirements of the radio frequency signal source and modulator are reduced, so the system cost is low. Attached Figure Description

[0023] The above and other objects, features, and advantages of the present invention will become readily apparent from the following detailed description of exemplary embodiments, taken in conjunction with the accompanying drawings. Several embodiments of the present invention are illustrated in the drawings by way of example and not limitation, in which:

[0024] Figure 1 This is a schematic diagram of the structure of a TGD-OFDR system based on broadband acousto-optic modulation to extend the frequency sweep range, as described in an embodiment of this utility model.

[0025] Figure 2 This is a time-frequency example diagram of the 2GHz sweep frequency range of the broadband acousto-optic modulator repeatedly modulated in an embodiment of this utility model. Detailed Implementation

[0026] The principles and spirit of this invention will now be described with reference to several exemplary embodiments. It should be understood that these embodiments are provided merely to enable those skilled in the art to better understand and implement this invention, and are not intended to limit the scope of this invention in any way. Rather, these embodiments are provided to make this disclosure more thorough and complete, and to fully convey the scope of this disclosure to those skilled in the art.

[0027] This utility model proposes a TGD-OFDR system based on broadband acousto-optic modulation to extend the frequency sweep range, as shown in the attached figure. Figure 1 The system includes a laser 1, a first fiber optic coupler 2, a semiconductor optical amplifier 3, a second fiber optic coupler 4, a broadband acousto-optic modulator 5, a third fiber optic coupler 6, an optical isolator 7, a photodetector 8, a fiber optic circulator 9, a fourth fiber optic coupler 10, a photoelectric balance detector 11, a data acquisition card 12, a computer 13, a radio frequency signal source 14, and a radio frequency correction unit 15.

[0028] The optical signal output terminal of laser 1 is connected to the optical signal input terminal of the first fiber coupler 2, and the optical signal output terminal of the first fiber coupler 2 is connected to the optical signal input terminal of semiconductor optical amplifier 3 and the optical signal input terminal of the fourth fiber coupler 10 respectively.

[0029] The optical signal output terminal of the semiconductor optical amplifier 3 is connected to the optical signal input terminal of the second fiber coupler 4. The optical signal output terminal of the second fiber coupler 4 is connected to port 9-1 of the fiber circulator 9 and the optical signal input terminal of the broadband acousto-optic modulator 5, respectively. The optical signal output terminal of the broadband acousto-optic modulator 5 is connected to the optical signal input terminal of the third fiber coupler 6. The optical signal output terminal of the third fiber coupler 6 is connected to the optical signal input terminal of the optical isolator 7 and the optical signal input terminal of the photodetector 8, respectively. The optical signal output terminal of the optical isolator 7 is connected to the optical signal input terminal of the second fiber coupler 4. Port 9-2 of the fiber circulator 9 is connected to the sensing fiber. Port 9-3 of the fiber circulator 9 is connected to the optical signal input terminal of the fourth fiber coupler 10.

[0030] The optical signal output terminal of the fourth fiber optic coupler 10 is connected to the optical signal input terminal of the photoelectric balance detector 11. The electrical signal output terminals of the photoelectric detector 8 and the photoelectric balance detector 11 are respectively connected to the data acquisition card 12 to acquire the passband. The data acquisition card 12 is connected to the computer 13. The RF output terminal of the RF signal source 14 is respectively connected to the RF signal input terminal of the semiconductor optical amplifier 3, the trigger signal input terminal of the data acquisition card 11, and the RF input terminal of the RF correction unit 15. The computer 13 is connected to the amplitude correction terminal of the RF correction unit 15. The RF output terminal of the RF correction unit 15 is connected to the optical signal input terminal of the broadband acousto-optic modulator 5.

[0031] In this embodiment, preferably, the laser 1 has a power of 10mW, a wavelength of 1550.12nm, and a linewidth of 500Hz.

[0032] In this embodiment, preferably, the first fiber coupler 2 and the third fiber coupler 6 are 1×2 couplers with a splitting ratio of 90:10; the second fiber coupler 4 and the fourth fiber coupler 10 are 2×2 couplers with a splitting ratio of 50:50.

[0033] In this embodiment, preferably, the semiconductor optical amplifier 3 is a gain-type modulator with an extinction ratio of 30dB; the broadband acousto-optic modulator 5 has a bandwidth of 100MHz and an extinction ratio of 50dB.

[0034] In this embodiment, preferably, the 3dB operating bandwidth of the photodetector 8 is 4GHz, and the 3dB operating bandwidth of the photoelectric balance detector 11 is 10GHz.

[0035] In this embodiment, preferably, the sampling rate of the data acquisition card 12 is 20GS / s and the sampling resolution is 14bit.

[0036] In this embodiment, the preferred operating process of the TGD-OFDR system is as follows:

[0037] The continuous light output from laser 1 is split into two paths by the first fiber coupler 2. The upper path serves as the probe light, and the lower path serves as the reference light. The continuous light in the upper path is modulated by the semiconductor optical amplifier 3 controlled by the radio frequency signal source 13. After outputting pulsed light, it is split 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 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, realizing flexible and controllable expansion of the frequency sweep range. After cyclic transmission and beam splitting, part of the pulsed light is injected into the sensing fiber through the fiber circulator 9, and the other part continues to undergo cyclic transmission and beam splitting.

[0038] During each cycle of transmission, the pulsed light signal undergoes linear frequency sweep modulation via broadband acousto-optic modulator 5. The frequency range of the pulsed light expands exponentially with the number of cycles, based on the linear frequency sweep range of broadband acousto-optic modulator 5. After linear frequency sweep modulation, the pulsed light passes through the third fiber coupler 6. A portion of the pulsed light continues its cyclic transmission via optical isolator 7 and the second fiber coupler 4, while the other portion undergoes photoelectric conversion via photodetector 8. The converted light is then recorded by data acquisition card 12 and transmitted to computer 13 for processing. Because the phase (frequency) information of the pulsed light is much greater than that of the photodetector... The response bandwidth of the device 8 detects the envelope amplitude information of the pulse light, but does not include the phase information of the pulse light. Based on the envelope information of the pulse light, the complementary envelope information of the pulse light is solved in real time and fed back to the RF correction unit 15. The RF correction unit 15 corrects the shape of the RF pulse input from the RF signal source 14 based on the complementary envelope information of the pulse light fed back by the computer 13. The corrected RF 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 of the pulse light.

[0039] The backscattered Rayleigh light signal in the sensing fiber is injected into the fourth fiber coupler 10 along with the lower reference light through the fiber optic circulator 9 for coherent beat frequency. The beat frequency result is 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 acquired linear sweep beat frequency result into a single-frequency signal through pulse compression.

[0040] At this point, the system's spatial resolution depends on the linear sweep range, which is flexibly achieved by repeated modulation of a low-bandwidth acousto-optic modulator. This avoids the use of high-bandwidth, high-performance modulators and RF signal sources, as well as sideband crosstalk; thus, high spatial resolution is achieved with flexible control over the sweep range at a lower cost. (Appendix) Figure 2 The time-frequency diagram of the sweep range of the broadband acousto-optic modulator with repetitive linear sweep modulation shows that the system extends the sweep range to 2 GHz at a relatively low cost.

[0041] The TGD-OFDR system based on broadband acousto-optic modulation to extend the frequency sweep range proposed in this utility model has the following advantages: 1) Flexible control of the frequency sweep range and high spatial resolution: The frequency sweep range of the system is flexibly achieved by repetitive linear modulation of a low-bandwidth acousto-optic modulator. The size of the frequency sweep range is related to the number of repetitions, and the frequency sweep range can be flexibly controlled by controlling the number of repetitions; the frequency sweep range determines the spatial resolution of the system, so the system has high spatial resolution. 2) Low system cost: The system flexibly achieves large-range linear frequency sweep modulation by repetitive linear modulation of a low-bandwidth acousto-optic modulator of tens / hundreds of megahertz. Compared with the method of using a large-bandwidth modulator and a high-performance RF signal source, the performance requirements of the RF signal source and modulator are reduced, and the system cost is low.

[0042] While the spirit and principles of this invention have been described with reference to several specific embodiments, it should be understood that this invention is not limited to the disclosed specific embodiments, and the division of aspects does not imply that features in these aspects cannot be combined for benefit; such division is merely for ease of description. This invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

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

2. The TGD-OFDR system based on broadband acousto-optic modulation to extend the frequency sweep range according to claim 1, characterized in that, The laser (1) has a power of 10mW, a wavelength of 1550.12nm, and a linewidth of 500Hz.

3. The TGD-OFDR system based on broadband acousto-optic modulation to extend the frequency sweep range according to claim 1, characterized in that, The first fiber coupler (2) and the third fiber coupler (6) are 1×2 couplers with a splitting ratio of 90:10; the second fiber coupler (4) and the fourth fiber coupler (10) are 2×2 couplers with a splitting ratio of 50:

50.

4. The TGD-OFDR system based on broadband acousto-optic modulation to extend the frequency sweep range according to claim 1, characterized in that, The extinction ratio of the semiconductor optical amplifier (3) is 30dB.

5. The TGD-OFDR system based on broadband acousto-optic modulation to extend the frequency sweep range according to claim 1, characterized in that, The broadband acousto-optic modulator (5) has a bandwidth of 100MHz and an extinction ratio of 50dB.

6. The TGD-OFDR system based on broadband acousto-optic modulation to extend the frequency sweep range according to claim 1, characterized in that, The 3dB operating bandwidth of the photodetector (8) is 4GHz.

7. The TGD-OFDR system based on broadband acousto-optic modulation to extend the frequency sweep range according to claim 1, characterized in that, The 3dB operating bandwidth of the photoelectric balance detector (11) is 10GHz.

8. The TGD-OFDR system based on broadband acousto-optic modulation to extend the frequency sweep range according to claim 1, characterized in that, The data acquisition card (12) has a sampling rate of 20GS / s and a sampling resolution of 14bit.

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