CN115876350A - Rapid Brillouin optical correlation domain analyzer based on optical frequency comb - Google Patents
Rapid Brillouin optical correlation domain analyzer based on optical frequency comb Download PDFInfo
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Abstract
The invention discloses a fast Brillouin optical correlation domain analyzer based on an optical frequency comb, belongs to the field of distributed optical fiber sensing, and solves the problem that the measurement speed of the existing Brillouin correlation domain analysis technology based on frequency scanning is limited. The analyzer takes a laser modulated by sinusoidal frequency as a system light source, opposite incidence of detection light and pumping light is carried out in an optical fiber to be detected, and stimulated Brillouin scattering is generated at a specific position of the optical fiber. The detection light is an optical frequency comb signal with a plurality of frequency components, the optical frequency comb signal is generated by driving an electro-optical modulator to modulate through an optical frequency comb module, and the frequency detection interval is regulated and controlled by a frequency conversion module. And after the detection optical frequency comb carrying the Brillouin gain information is subjected to filtering detection, the Brillouin frequency shift is extracted through frequency domain analysis, and finally the sensing information of the optical fiber link to be detected is obtained. The system of the invention does not need to sweep frequency, improves the measuring speed and has the dynamic measuring capability of high spatial resolution.
Description
Technical Field
The invention belongs to the field of distributed optical fiber sensing, and particularly relates to a fast Brillouin optical correlation domain analyzer based on an optical frequency comb.
Background
The distributed optical fiber sensing technology uses an optical fiber as a sensing medium, and can realize distributed measurement of sensing parameters along an optical fiber link by using different backscattering effects and distributed positioning technologies, and the distributed optical fiber sensing technology is widely applied to various fields of security systems, structure monitoring, pipeline monitoring, manufacturing industries and the like. Among them, the brillouin optical correlation domain analyzer based on the stimulated brillouin scattering effect has excellent characteristics of high spatial resolution, high measurement accuracy and arbitrary addressing, and has been receiving wide attention and research in recent years.
In a traditional sinusoidal frequency modulation Brillouin optical correlation domain analyzer, detection light and pumping light which are subjected to sinusoidal frequency modulation are oppositely incident into a sensing optical fiber, and a periodic correlation peak is generated at a specific position of the optical fiber. When the frequency difference of the two beams of light approaches the Brillouin frequency shift of the current optical fiber position, the stimulated Brillouin scattering effect caused at the non-correlation peak is weak, the stimulated Brillouin scattering effect caused at the correlation peak is strong, and the probe light obtains narrow-band gain. Therefore, after the modulation frequency is adjusted to enable the sensing optical fiber to have a unique correlation peak, the brillouin gain spectrum corresponding to the position of the correlation peak can be obtained by continuously adjusting the frequency of the probe light. If distributed sensing is to be realized, modulation frequency scanning and probe light frequency scanning need to be performed alternately. But is limited by the frequency switching time of the microwave source, and the two time-consuming frequency sweeping operations greatly limit the measurement speed of the sensing system.
To improve dynamic measurement performance, various solutions are proposed. One scheme is to replace the traditional microwave source with a voltage-controlled oscillator with extremely short frequency switching time and match with a high-bandwidth phase-locked amplifier, so that the frequency scanning of the detection light can be completed within a very short time, but the detection light is limited by the working bandwidth of the phase-locked amplifier, and the measurement speed of the scheme is difficult to further improve. Another solution is to use a differential detection structure in combination with injection locking technology to avoid the use of a lock-in amplifier, and simultaneously scan the modulation frequency during scanning the detection light frequency to eliminate the time consumption of position scanning, but the measurement speed of this solution is limited by the modulation frequency of the light source. In order to realize frequency sweep-free, one scheme is to adopt a double-slope auxiliary method, the slope of the Brillouin gain spectrum is regarded as a linear interval, and Brillouin frequency shift is demodulated by monitoring probe light with fixed frequency. Therefore, how to further increase the measurement speed without sacrificing the measurement accuracy of the system is urgently needed to be solved.
Disclosure of Invention
Aiming at the defects and improvement requirements of the prior art, the invention provides a fast Brillouin optical correlation domain analyzer based on an optical frequency comb, and aims to solve the technical problem that the measurement speed of the existing Brillouin optical correlation domain analyzer is limited.
In order to achieve the above object, the present invention provides a fast brillouin optical correlation domain analyzer based on an optical frequency comb, comprising: the device comprises a laser, a microwave source, a coupler, a frequency conversion module, an electro-optic modulator, an optical frequency comb module, a first erbium-doped fiber amplifier, an isolator, an optical fiber to be tested, a delay fiber, a second erbium-doped fiber amplifier, a circulator, a filtering module, a photoelectric detector and a data acquisition module;
the sinusoidal frequency signal generated by the microwave source directly modulates the current of the laser, and the output light of the laser is used as a system light source and is divided into two paths by the coupler to respectively generate probe light and pump light;
in the detection light path, the frequency conversion module shifts the frequency of the detection light to adjust the frequency detection interval of the detection light; the optical frequency comb module generates a digital electrical frequency comb signal to drive the electro-optical modulator to modulate the frequency-shifted detection light, and the generated detection optical frequency comb enters one end of an optical fiber to be detected through the isolator after being amplified by the first erbium-doped optical fiber amplifier;
in the pumping light path, the pumping light enters the other end of the optical fiber to be detected through the circulator after being delayed and amplified by the delay optical fiber and the second erbium-doped optical fiber amplifier;
and the detection optical frequency comb carrying the stimulated Brillouin scattering signal is output by the circulator, filtered to remove noise by the filtering module and collected by the data acquisition module after passing through the photoelectric detector.
Further, the digital electrical frequency comb signals generated by the optical frequency comb module have equal frequency intervals.
Further, the frequency conversion module is configured to adjust a frequency difference between the probe light and the pump light, so that a frequency detection range of the probe optical frequency comb covers a brillouin frequency shift of the optical fiber to be detected.
Further, the filtering bandwidth of the filtering module is greater than the sum of the modulation amplitude of the laser and the bandwidth of the detection optical frequency comb.
Further, the laser is a distributed feedback semiconductor laser with a narrow linewidth.
Further, the length of the delay optical fiber is matched with that of the optical fiber to be detected, so that a unique correlation peak exists in the optical fiber to be detected.
Further, the data acquisition module is also used for digital signal processing, and the stimulated brillouin scattering signal is extracted in a frequency domain to obtain temperature or strain information of the optical fiber link to be detected.
Generally, by the above technical solution conceived by the present invention, the following beneficial effects can be obtained:
(1) According to the fast Brillouin optical correlation domain analyzer based on the optical frequency comb, the optical frequency comb is used as detection light, and a Brillouin gain spectrum is obtained at one time on a frequency domain by utilizing the multi-frequency parallel transmission characteristic of the optical frequency comb, so that single frequency sweep in the existing correlation domain analysis system is avoided. In addition, different from intensity demodulation in the existing correlation domain analysis system, sensing information demodulation is realized by relying on digital signal processing on a frequency domain, and the correlation domain analyzer provided by the invention does not need to use a phase-locked amplifier and a pulse modulation device of pump light, so that the system structure is simplified, and the problem that the measurement speed in the existing correlation domain analysis system is limited by the frequency sweep rate of a microwave source and the bandwidth of the phase-locked amplifier is solved.
(2) The single-point sampling speed of the related domain analyzer provided by the invention only depends on the frame length of the optical frequency comb, and the sensing precision configuration is flexible. The dynamic measurement capability of the Brillouin correlation domain analyzer can be improved under the condition of not sacrificing the system precision, and the rapid measurement of the optical fiber distributed temperature and strain in a high dynamic range is realized.
Drawings
FIG. 1 is a schematic structural diagram of a fast Brillouin optical correlation domain analyzer based on an optical frequency comb according to the present invention;
in the figure:
11. a laser; 12. a microwave source; 13. a coupler; 14. a frequency conversion module; 15. an electro-optic modulator; 16. an optical frequency comb module; 17. a first erbium-doped fiber amplifier; 18. an isolator; 19. an optical fiber to be tested; 20. a delay fiber; 21. a second erbium-doped fiber amplifier; 22. a circulator; 23. a filtering module; 24. a photodetector; 25. and a data acquisition module.
Fig. 2 is a single-position single-frame signal brillouin gain spectrum experimental result diagram of the fast brillouin optical correlation domain analyzer based on the optical frequency comb.
Fig. 3 is a single-position multi-frame signal brillouin gain spectrum experimental result diagram of the fast brillouin optical correlation domain analyzer based on the optical frequency comb.
Fig. 4 is a diagram of a result of a distributed brillouin frequency shift measurement experiment of a fast brillouin optical correlation domain analyzer based on an optical frequency comb.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
In the present application, the terms "first," "second," and the like (if any) in the description and the drawings are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order.
The first embodiment is as follows:
referring to fig. 1, the fast brillouin optical correlation domain analyzer based on optical frequency comb provided in this embodiment includes a laser 11, a microwave source 12, a coupler 13, a frequency conversion module 14, an electro-optical modulator 15, an optical frequency comb module 16, a first erbium-doped fiber amplifier 17, an isolator 18, an optical fiber to be measured 19, a delay fiber 20, a second erbium-doped fiber amplifier 21, a circulator 22, a filtering module 23, a photodetector 24, and a data acquisition module 25.
In this example, the laser 11 is a distributed feedback semiconductor laser operating at a wavelength around 1550nm, with a linewidth of 100kHz, current-modulated directly by a sinusoidal signal output from the microwave source 12. The modulation frequency and the modulation amplitude of the sinusoidal frequency modulation are respectively set to be 2.85MHz and 3.42GHz, and the corresponding system measurement range and the theoretical spatial resolution are respectively 36m and 10cm. The output light of the laser 11 is split into two paths by the 3dB coupler 13.
In the detection light path, the frequency conversion module 14 is composed of a microwave synthesizer, a single-sideband modulator and an injection locking device, wherein the microwave synthesizer generates a microwave signal of 8.1GHz and drives the single-sideband modulator to carry out down-conversion on a carrier wave. In order to improve the signal-to-noise ratio of the system, the output light of the single-sideband modulator is amplified by the injection locking device and other spectral components are suppressed. The optical frequency comb module 16 generates a plurality of frames of digital electrical frequency combs with the same frequency interval through an arbitrary waveform generator, drives the electro-optical modulator 15 to perform double-sideband modulation on output light of the frequency conversion module 14, generates a detection optical frequency comb with a frequency detection range covering Brillouin frequency shift of an optical fiber 19 to be detected, and the detection optical frequency comb enters one end of the optical fiber 19 to be detected through the isolator 18 after being amplified by the first erbium-doped optical fiber amplifier 17.
In the pumping light path, the delay fiber 20 is used to control the correlation peak, so that the only correlation peak exists on the fiber 19 to be measured, and the only correlation peak is amplified by the second erbium-doped fiber amplifier 21 and then enters the other end of the fiber 19 to be measured through the port 1-2 of the circulator 22.
After the probe light interacts with the pump light in the optical fiber to be measured, the probe light comb carrying the stimulated Brillouin scattering signal reaches an optical filtering module 23 through a port 2-3 of a circulator 22, photoelectric conversion is completed through a photoelectric detector 24 with the bandwidth of 1.6GHz after noise is filtered, a receiving frequency comb is obtained after the signals are collected and averaged for 100 times through a data collecting module 25, the stimulated Brillouin scattering signal is extracted from each frame of signal in a frequency domain by using a digital signal processing algorithm, brillouin frequency shift is calculated, and temperature or strain information of the optical fiber link to be measured is obtained.
As an example, a 20m polarization maintaining fiber having a brillouin frequency shift in the vicinity of 10.35GHz was used for the test as the optical fiber to be tested. In a detection light path, the initial frequency of the digital optical frequency comb is 1GHz, the frequency interval is 2MHz, the frequency number is 300, the frame length is 0.5 mu s, the frame number is 200, and the measurement frequency range of the detection optical frequency comb is 10.1 GHz-10.7 GHz. In the pumping optical path, the length of the delay fiber is set to 300m.
The result of performing brillouin spectrum extraction on a single frame signal by using a receiving frequency comb without obtaining brillouin gain as background noise is shown in fig. 2, and the single-point sampling rate of the system reaches 20kSa/s. The brillouin spectral measurement of a single 200 frame signal at a single correlation peak position is shown in figure 3. In order to prove the distributed sensing performance of the system, the modulation frequency is scanned from 2.65MHz to 2.88MHz, the Brillouin frequency shift measured by the system is shown in figure 4, the optical fiber section with the Brillouin frequency shift close to 10.7GHz is a tail fiber, and a 10cm stretching section of the tail end of the optical fiber to be measured is clearly measured, which shows that the spatial resolution of the sensing system can reach 10cm.
The second embodiment:
the difference between the first embodiment and the second embodiment is that the high-bandwidth optical frequency comb module is used for generating the high-frequency digital electrical frequency comb, and the high-bandwidth electro-optical modulator is used for detecting the optical frequency comb modulation, so that a frequency conversion module is not needed, and the system complexity is reduced.
Example three:
the difference between this embodiment and the first embodiment is that the frequency conversion module is moved to the pump optical path, and the frequency detection interval of the probe light is adjusted by up-conversion of the pump light to cover the brillouin frequency shift of the optical fiber to be measured.
In summary, the optical frequency comb-based fast brillouin optical correlation domain analyzer of the present invention uses the optical frequency comb as probe light, replaces the traditional single frequency scanning operation, has a large measurement range and flexible system precision configuration, breaks through the measurement speed limitation of the existing fast measurement scheme, and can further improve the dynamic measurement capability of the brillouin optical correlation domain analyzer.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (7)
1. A fast Brillouin optical correlation domain analyzer based on an optical frequency comb is characterized by comprising the following components: the device comprises a laser, a microwave source, a coupler, a frequency conversion module, an electro-optical modulator, an optical frequency comb module, a first erbium-doped fiber amplifier, an isolator, an optical fiber to be tested, a delay optical fiber, a second erbium-doped fiber amplifier, a circulator, a filtering module, a photoelectric detector and a data acquisition module;
the sinusoidal frequency signal generated by the microwave source directly modulates the current of the laser, and the output light of the laser is used as a system light source and is divided into two paths by the coupler, and the two paths are used for generating detection light and pumping light respectively;
in the detection light path, the frequency conversion module shifts the frequency of the detection light to adjust the frequency detection interval of the detection light; the optical frequency comb module generates a digital electrical frequency comb signal to drive the electro-optical modulator to modulate the frequency-shifted detection light, and the generated detection optical frequency comb enters one end of an optical fiber to be detected through the isolator after being amplified by the first erbium-doped optical fiber amplifier;
in the pumping light path, the pumping light enters the other end of the optical fiber to be detected through the circulator after being delayed and amplified by the delay optical fiber and the second erbium-doped optical fiber amplifier;
the detection optical frequency comb carrying the stimulated Brillouin scattering signal is output by the circulator, noise is filtered by the filtering module, and the detection optical frequency comb passes through the photoelectric detector and is collected by the data collecting module.
2. The optical-frequency-comb-based fast brillouin optical correlation domain analyzer in accordance with claim 1, wherein the digital electrical frequency comb signals generated by the optical-frequency comb module have equal frequency intervals.
3. The fast Brillouin optical correlation domain analyzer based on the optical-frequency comb according to claim 1, wherein the frequency conversion module is configured to adjust a frequency difference between the probe light and the pump light, so that a frequency detection range of the probe optical-frequency comb covers a Brillouin frequency shift of the optical fiber under test.
4. The fast brillouin optical correlation domain analyzer based on an optical-frequency comb according to claim 1, wherein a filtering bandwidth of the filtering module is larger than a sum of a modulation amplitude of the laser and a bandwidth of the probing optical-frequency comb.
5. The optical-frequency-comb-based fast brillouin optical correlation domain analyzer in accordance with claim 1, wherein said laser is a distributed feedback semiconductor laser with narrow linewidth.
6. The fast brillouin optical correlation domain analyzer based on optical frequency comb according to claim 1, wherein the length of the delay fiber is matched with the length of the optical fiber to be measured to ensure that there is a unique correlation peak in the optical fiber to be measured.
7. The optical frequency comb-based rapid Brillouin optical correlation domain analyzer according to claim 1, wherein the data acquisition module is further configured to perform digital signal processing to extract the stimulated Brillouin scattering signal in a frequency domain to obtain temperature or strain information of the optical fiber link to be measured.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116337777A (en) * | 2023-05-29 | 2023-06-27 | 之江实验室 | Broadband photoacoustic spectrum measurement system and method based on single optical comb |
| CN116972891A (en) * | 2023-09-25 | 2023-10-31 | 华中科技大学 | Quick Brillouin optical correlation domain analyzer based on multi-core optical fiber |
| CN117490741A (en) * | 2024-01-03 | 2024-02-02 | 华中科技大学 | Quick Brillouin optical time domain analyzer based on double-sideband optical frequency comb |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116337777A (en) * | 2023-05-29 | 2023-06-27 | 之江实验室 | Broadband photoacoustic spectrum measurement system and method based on single optical comb |
| CN116337777B (en) * | 2023-05-29 | 2023-08-29 | 之江实验室 | Broadband photoacoustic spectrum measurement system and method based on single optical comb |
| CN116972891A (en) * | 2023-09-25 | 2023-10-31 | 华中科技大学 | Quick Brillouin optical correlation domain analyzer based on multi-core optical fiber |
| CN116972891B (en) * | 2023-09-25 | 2023-11-28 | 华中科技大学 | Quick Brillouin optical correlation domain analyzer based on multi-core optical fiber |
| CN117490741A (en) * | 2024-01-03 | 2024-02-02 | 华中科技大学 | Quick Brillouin optical time domain analyzer based on double-sideband optical frequency comb |
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