5GHz Brillouin optical fiber sensing frequency sweeping system

Abstract

The utility model relates to a 5GHz Brillouin optical fiber sensing frequency sweeping system. Comprising a narrow linewidth laser, a microwave signal source, a first electrooptical modulator, a beam splitter, an acousto-optic modulator, a pulse erbium-doped optical fiber amplifier, an optical filter, a microwave signal source, a second electrooptical modulator, a scrambler, a variable optical attenuator, a sensing optical fiber, an optical circulator, a photoelectric detector and a data acquisition card. According to the Brillouin optical fiber sensing frequency sweeping system, a 5GHz electro-optical modulator is mainly adopted to modulate a narrow linewidth laser, a high-frequency sideband and a low-frequency sideband are generated and are respectively used as pump light and probe light of an optical fiber sensing system, and strain and temperature along an optical fiber link are monitored in a fixed-point and quantitative manner by utilizing stimulated Brillouin scattering of an optical fiber. The system is simple in structure and low in cost, and has excellent measurement precision and signal-to-noise ratio.

Description

Technical Field

[0001] The utility model relates to the field of optical fiber sensing, and particularly to a 5GHz Brillouin optical fiber sensing frequency-sweeping system. Background Art

[0002] Distributed optical fiber sensing systems based on the Brillouin scattering effect have become a hot sensing technology in recent years. By detecting the Brillouin frequency shift in the optical fiber, the changes in temperature and strain along the entire optical fiber link can be detected, and it has broad application prospects in the real-time safety monitoring of large-scale building facilities such as oil well pipelines, bridges, and tunnels.

[0003] Currently, the Brillouin time-domain analysis system (BOTDA) mainly generates stimulated Brillouin scattering in the optical fiber by using continuous probe light and pulsed pump light. By measuring the frequency shift and linewidth of the Brillouin scattering signal gain peak and fitting the measured data with a fitting algorithm, the measurement of the temperature and stress of the optical fiber link is completed. However, this traditional detection method requires the use of a high-frequency microwave source to shift the frequency of the incident light by about 11HGz to generate the stimulated Brillouin scattering effect, which results in disadvantages such as high system cost and low measurement accuracy. Summary of the Utility Model

[0004] To solve the technical problems existing in the prior art, the utility model provides a 5GHz Brillouin optical fiber sensing frequency-sweeping system to reduce the system cost, improve the signal-to-noise ratio and measurement accuracy of the system.

[0005] To achieve the above object, the technical solution of the utility model is as follows:

[0006] A 5GHz Brillouin optical fiber sensing frequency-sweeping system includes a narrow linewidth laser, a first electro-optic modulator, a beam splitter, an acousto-optic modulator, a pulsed erbium-doped fiber amplifier, an optical filter, a second electro-optic modulator, a polarization scrambler, a variable optical attenuator, a sensing optical fiber, an optical circulator, a photodetector, and a data acquisition card. The optical circulator has three ports. The narrow linewidth laser is connected to the input end of the first electro-optic modulator. The output end of the first electro-optic modulator is connected to the beam splitter. There are two paths of light split from the beam splitter. One path of the laser is used as pulsed light and is connected to the input ends of the acousto-optic modulator, the pulsed erbium-doped fiber amplifier, and the optical filter. The output end of the optical filter is connected to the sensing optical fiber. The sensing optical fiber is connected to the first port of the optical circulator. The other path of the laser split from the beam splitter is used as probe light and is connected to the input end of the second electro-optic modulator. The output end of the second electro-optic modulator is connected to the input end of the polarization scrambler. The output end of the polarization scrambler is connected to one end of the variable optical attenuator. The other end of the variable optical attenuator is connected to the second port of the optical circulator. The third port of the optical circulator is connected to the receiving end of the photodetector. The output end of the photodetector is connected to the data acquisition card.

[0007] As a preferred technical solution, the system further includes a first microwave signal source and a second microwave signal source. The first microwave signal source is connected to the control end of the first electro-optic modulator through a signal line, and the second microwave signal source is connected to the control end of the second electro-optic modulator through a signal line.

[0008] As a preferred technical solution, the central wavelength of the narrow linewidth laser is 1550 nm, and the spectral linewidth is less than 3 kHz.

[0009] As a preferred technical solution, the components in the system are connected by single-mode optical fibers.

[0010] As a preferred technical solution, the modulation frequency of the first electro-optic modulator is 5 GHz, and the sweep frequency range of the second electro-optic modulator is 200 MHz.

[0011] As a preferred technical solution, the splitting ratio of the beam splitter is 50:50.

[0012] As a preferred technical solution, a working method of a 5 GHz Brillouin optical fiber sensing sweep system includes the following steps:

[0013] The first electro-optic modulator modulates the laser generated by the narrow linewidth laser to generate a high-frequency sideband with a frequency of ν L +ν 1 and a low-frequency sideband with a frequency of ν L -ν 1 , where ν L is the laser frequency of 1550 nm generated by the narrow linewidth laser, and ν 1 is the frequency shift frequency of the laser of 5 GHz;

[0014] When the second electro-optic modulator sweeps the frequency under the modulation of the second microwave signal source, when the scanned frequency difference is equal to the Brillouin frequency shift, energy conversion occurs in the sensing optical fiber to obtain a Brillouin spectrum, thereby realizing the measurement of distributed sensing temperature and strain parameters.

[0015] As a preferred technical solution, the pulsed light and the continuous detection light generate a stimulated Brillouin effect in the sensing optical fiber, and are detected by a photodetector connected to the third port of the optical circulator, and then collected by a data acquisition card to obtain Brillouin spectral lines related to temperature and strain.

[0016] Compared with the prior art, the beneficial effects of the present utility model are:

[0017] The 5GHz Brillouin fiber optic sensing frequency-sweeping system of the present utility model is modulated by a first electro-optic modulator after a narrow linewidth laser to generate two sidebands, a high-frequency sideband and a low-frequency sideband. After filtering out the high-frequency signal, the low-frequency signal undergoes stimulated Brillouin scattering in the sensing fiber. Therefore, only a frequency shift of about 5GHz is required, greatly reducing the cost of the system and making the structure more compact and small. The frequency-sweeping range of the probe light is set at 200MHz, which shortens the measurement time while ensuring the measurement accuracy and stability of the entire sensing system. Since the frequency-sweeping range is small, the system cost is also reduced. Brief Description of the Drawings

[0018] Figure 1 is a schematic structural diagram of the Brillouin fiber optic sensing frequency-sweeping system of the present utility model;

[0019] Figure 2 is a schematic frequency-domain principle diagram of the Brillouin fiber optic sensing frequency-sweeping system of the present utility model.

[0020] In the figure: 1. Narrow linewidth laser; 2. First microwave signal source; 3. First electro-optic modulator; 4. Beam splitter; 5. Acousto-optic modulator; 6. Pulse erbium-doped fiber amplifier; 7. Optical filter; 8. Second microwave signal source; 9. Second electro-optic modulator; 10. Polarization scrambler; 11. Variable optical attenuator; 12. Sensing fiber; 13. Optical circulator; 14. Photoelectric detector; 15. Data acquisition card. Detailed Embodiments

[0021] The technical solution of the present utility model will be further described below in conjunction with the detailed embodiments:

[0022] As Figure 1 shown, a 5GHz Brillouin fiber optic sensing frequency-sweeping system includes a narrow linewidth laser 1, a first electro-optic modulator 3, a beam splitter 4, an acousto-optic modulator 5, a pulse erbium-doped fiber amplifier 6, an optical filter 7, a second electro-optic modulator 9, a polarization scrambler 10, a variable optical attenuator 11, a sensing fiber 12, an optical circulator 13, a photoelectric detector 14, and a data acquisition card 15.

[0023] After the laser generated by the narrow linewidth laser 1 passes through the first electro-optic modulator 3, it is split into two paths by the beam splitter 4. One path of the laser is used as pulsed light. After the acousto-optic modulator 5 generates optical pulses, the pulsed light is amplified by the pulsed erbium-doped fiber amplifier 6. After passing through the optical filter 7 to pass the 1550 nm + 5 GHz signal and filtering out the 1550 nm - 5 GHz signal, it enters the sensing fiber 12 through the first port of the optical circulator 13 to generate stimulated Brillouin signals; the other path of the laser is used as the probe light, which sequentially passes through the second electro-optic modulator 9, the polarization scrambler 10, and the variable optical attenuator 11 and then is connected to the sensing fiber 12 and the second port of the optical circulator 13. The system also includes a first microwave signal source 2 and a second microwave signal source 8. The first microwave signal source 2 is connected to the control end of the first electro-optic modulator 3 through a signal line, and the second microwave signal source 8 is connected to the control end of the second electro-optic modulator 9 through a signal line.

[0024] The first electro-optic modulator 3 modulates the laser generated by the narrow linewidth laser 1 to generate a high-frequency sideband with a frequency of ν L +ν 1 and a low-frequency sideband with a frequency of ν L -ν 1 , where ν L is the laser frequency 1550 nm of the laser generated by the narrow linewidth laser 1, and ν 1 is the frequency shift frequency 5 GHz of the laser.

[0025] After the acousto-optic modulator 5 generates optical pulses, the pulsed light is amplified by the pulsed erbium-doped fiber amplifier 6. After passing through the optical filter 7, it is transmitted to one end of the sensing fiber 12 to generate 1550 nm - 5 GHz and 1550 nm + 15 GHz signals; the second electro-optic modulator 9 is driven by the second microwave signal source 8 to sweep the frequency by 200 MHz around 1550 nm - 5 GHz to track and sweep the stimulated Brillouin signals related to the external temperature and strain.

[0026] The third port of the optical circulator 13 is sequentially connected to the photodetector 14 and the data acquisition card 15. After the stimulated Brillouin scattered light generated by the pulsed light is detected and energy-converted, it is demodulated by digital signal processing to obtain the temperature or strain changes occurring along the sensing fiber 12 link. That is, the pulsed light and the continuous probe light generate the stimulated Brillouin effect in the sensing fiber 12, and are detected by the photodetector 14 connected to the third port of the optical circulator 13, and then collected by the data acquisition card 15 to obtain the Brillouin spectrum related to temperature and strain.

[0027] Specifically, the narrow linewidth laser 1 outputs through a polarization-maintaining fiber. The beam splitter 4 is a 1×2 fiber polarization-maintaining coupler with a splitting ratio of 50:50. The beam splitter 4 is sequentially connected to the acousto-optic modulator 5 and the pulsed erbium-doped fiber amplifier 6 by single-mode fibers. The second electro-optic modulator 9 is sequentially connected to the depolarizer 10, the variable optical attenuator 11, and the first port of the optical circulator 13 by single-mode fibers.

[0028] Specifically, the central wavelength of the narrow linewidth laser 1 is 1550 nm, and the spectral linewidth is less than 3 kHz.

[0029] As Figure 2 shown, it is the frequency-domain schematic diagram in the embodiment of the present invention. In this example, the laser frequency of the narrow linewidth laser 1 is ν L , under the modulation of the first electro-optic modulator 3, high-frequency sidebands with a frequency of ν L +ν 1 and low-frequency sidebands with a frequency of ν L -ν 1 are generated.

[0030] When the second electro-optic modulator 9 performs frequency sweeping under the modulation of the second microwave signal source 8, when the frequency difference is scanned to be equal to the Brillouin frequency shift, after energy conversion in the sensing fiber 12, a Brillouin spectrum is generated, thereby realizing the measurement of distributed sensing temperature and strain parameters.

[0031] This embodiment is only a further explanation of the present invention and does not limit the present invention. Those skilled in the art can make non-creative modifications to this embodiment as needed after reading this specification, but as long as it is within the scope of the claims of the present invention, it is protected by the patent law.

Claims

1. A 5 GHz Brillouin optical fiber sensing sweep frequency system, characterized in that: The invention comprises a narrow line width laser, a first electro-optic modulator, a beam splitter, an acousto-optic modulator, a pulsed erbium-doped fiber amplifier, an optical filter, a second electro-optic modulator, a polarization scrambler, a variable optical attenuator, a sensing optical fiber, an optical circulator, a photodetector and a data acquisition card. The optical circulator is provided with three ports. The narrow line width laser is connected to the input end of the first electro-optic modulator, the output end of the first electro-optic modulator is connected to the beam splitter, and the light split from the beam splitter has two paths, one of which is a laser as a pulse light and is connected to the input end of the acousto-optic modulator, the pulsed erbium-doped fiber amplifier and the optical filter. The output end of the optical filter is connected to the sensing optical fiber, and the sensing optical fiber is connected to the first port of the optical circulator; another laser divided by the beam splitter is used as a detection light and connected to the input end of the second electro-optical modulator, the output end of the second electro-optical modulator is connected to the input end of the polarization scrambler, the output end of the polarization scrambler is connected to one end of the variable optical attenuator, the other end of the variable optical attenuator is connected to the second port of the optical circulator, the third port of the optical circulator is connected to the receiving end of the photodetector, and the output end of the photodetector is connected to the data acquisition card.

2. The 5 GHz Brillouin optical fiber sensing sweep frequency system according to claim 1, characterized in that: The system also includes a first microwave signal source and a second microwave signal source, wherein the first microwave signal source is connected to the control end of the first electro-optic modulator through a signal line, and the second microwave signal source is connected to the control end of the second electro-optic modulator through a signal line.

3. The 5 GHz Brillouin optical fiber sensing sweep frequency system according to claim 1, characterized in that: The central wavelength of the narrow linewidth laser is 1550nm, and the spectral linewidth is less than 3kHz.

4. The 5 GHz Brillouin optical fiber sensing sweep frequency system according to claim 1, characterized in that: The components in the system are connected via single-mode optical fibers.

5. The 5 GHz Brillouin optical fiber sensing sweep frequency system according to claim 1, characterized in that: The modulation frequency of the first electro-optic modulator is 5 GHz, and the sweep frequency range of the second electro-optic modulator is 200 MHz.

6. The 5 GHz Brillouin optical fiber sensing sweep frequency system according to claim 1, characterized in that: The beam splitter has a splitting ratio of 50:50.

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