CN117213537B - Gain differential measurement type high performance chaotic Brillouin sensing device and method - Google Patents
Gain differential measurement type high performance chaotic Brillouin sensing device and method Download PDFInfo
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Abstract
本发明涉及分布式光纤传感领域，公开了一种增益差分测量型高性能混沌布里渊传感装置及方法。装置中混沌激光源的输出被分为第一和第二混沌激光，第一混沌激光依次经过单边带调制器、掺铒光纤放大器、第二分束器后分为探测光和差分参考光，探测光入射到传感光纤的一端并从另一端经第一光环行器输出被第一光电探测器探测，差分参考光被第二光电探测器探测；第二混沌激光依次经光延迟线、半导体光放大器、第三分束器后分为泵浦光和互相关参考光，泵浦光放大后从另一端注入传感光纤，互相关参考光被第三光电探测器探测；三路探测信号经计算机进行数据处理。本发明可抑制混沌强度噪声的干扰，提高系统信噪比，在保证高空间分辨率同时拓宽传感距离。
The present invention relates to the field of distributed optical fiber sensing, and discloses a gain differential measurement type high-performance chaotic Brillouin sensing device and method. The output of a chaotic laser source in the device is divided into a first and a second chaotic laser. The first chaotic laser is sequentially divided into a detection light and a differential reference light after passing through a single-sideband modulator, an erbium-doped optical fiber amplifier, and a second beam splitter. The detection light is incident on one end of the sensing optical fiber and outputted from the other end through a first optical circulator to be detected by a first photodetector, and the differential reference light is detected by a second photodetector; the second chaotic laser is sequentially divided into a pump light and a cross-correlation reference light after passing through an optical delay line, a semiconductor optical amplifier, and a third beam splitter. The pump light is amplified and injected into the sensing optical fiber from the other end, and the cross-correlation reference light is detected by a third photodetector; the three-way detection signal is processed by a computer. The present invention can suppress the interference of chaotic intensity noise, improve the system signal-to-noise ratio, and broaden the sensing distance while ensuring high spatial resolution.
Description
Technical Field
The invention relates to the field of distributed optical fiber sensing, in particular to a gain differential measurement type high-performance chaotic Brillouin sensing device and method.
Background
Distributed optical fiber sensing technology is one of the high and new technologies that are attracting attention and developing rapidly in the world today. The method is an important support for constructing a novel infrastructure safety guarantee network with high speed ubiquitous, integrated and interconnected, safety and high efficiency in national planning. The distributed optical fiber sensing technology has unique strategic value and huge economic benefit, and plays an irreplaceable role in the fields of submarine seismic monitoring, oil and gas resource exploration, military border security and the like.
In a distributed optical fiber Brillouin sensing system, spatial resolution and sensing distance are important technical indexes, the spatial resolution reflects the minimum length of the applied temperature and strain of an optical fiber which can be resolved by the sensing system, and the sensing distance is the maximum distance of the effective sensing of the system. At present, the traditional time domain gating type chaotic Brillouin Optical Correlation Domain Analysis (BOCDA) technology adopts traditional chaotic laser as a light source, so that the power of pulse light cannot be too high to avoid nonlinear effects, the energy loss of the pulse light is serious along with the increase of the sensing distance, the Brillouin gain signal at the tail end of an optical fiber is extremely weak due to chaotic light intensity noise, the chaotic light intensity noise is extremely easy to submerge in the intensity noise of the chaotic light, and long-distance accurate positioning is difficult to realize.
Therefore, it is necessary to invent a high-performance chaotic Brillouin distributed optical fiber sensing technology, which suppresses the interference of chaotic intensity noise on gain information, improves the signal-to-noise ratio of the system, and meets the requirement of long distance and high spatial resolution.
Disclosure of Invention
The invention provides a gain difference measurement type chaotic Brillouin sensing device and a method, which aim to improve the signal-to-noise ratio of a sensing system and expand the sensing distance while ensuring high spatial resolution, and solve the problem that the sensing distance is limited and expanded by chaotic intensity noise interference gain information in the existing chaotic BOCDA system.
The technical scheme includes that the gain difference measurement type high-performance chaotic Brillouin sensing device comprises a chaotic laser source, wherein chaotic laser output by the chaotic laser source is divided into first chaotic laser and second chaotic laser through a first beam splitter, the first chaotic laser sequentially passes through a single-sideband modulator and an erbium-doped optical fiber amplifier and then is divided into detection light and differential reference light through a second beam splitter, the detection light is incident to one end of a sensing optical fiber, the differential reference light is detected by a second photoelectric detector, the second chaotic laser sequentially passes through an optical delay line and a semiconductor optical amplifier and then is divided into pump light and cross-correlation reference light through a third beam splitter, the pump light is injected from the other end of the sensing optical fiber through a first optical circulator after being optically amplified, the cross-correlation reference light is detected by a third photoelectric detector, and a transmission signal in the sensing optical fiber is output through the first optical circulator and then is detected by the first photoelectric detector;
The single-sideband modulator is used for modulating the first chaotic laser to generate frequency downshifting, and the downshifting amount is equal to the Brillouin frequency shift amount in the sensing optical fiber; the erbium-doped fiber amplifier is used for amplifying the first chaotic laser after the frequency is shifted down; the optical delay line is used for adjusting the delay of the second chaotic laser, and the semiconductor optical amplifier is used for modulating the continuous second chaotic laser into pulse chaotic light;
The three detection signals are synchronously collected by the data collection unit and sent to the computer for data processing.
The specific method for the computer to process the data comprises the following steps:
performing cross-correlation operation on the transmission signal detected by the first photoelectric detector and the differential reference signal detected by the second photoelectric detector to obtain an optical path difference of two paths of signals;
Then carrying out optical path difference matching on the transmission signal and the differential reference signal, and carrying out differential operation on the transmission signal and the differential reference signal after the optical path difference matching to obtain chaotic Brillouin gain information;
And carrying out cross-correlation operation on the obtained chaotic Brillouin gain information and a cross-correlation reference signal detected by the third photoelectric detector, so as to realize the positioning of a correlation peak.
The chaotic laser source comprises a laser, an optical fiber ring oscillator and a feedback loop, wherein laser emitted by the laser is incident to the feedback loop through the optical fiber ring oscillator, the feedback loop is used for feeding back an incident laser part to the optical fiber ring oscillator and the laser in sequence to enable the laser to output chaotic laser, the chaotic laser output by the laser is output after passing through the optical fiber ring oscillator and the feedback loop, and the optical fiber ring oscillator is used for lifting low-frequency energy in the chaotic laser output by the laser.
The feedback loop comprises a second optical circulator, a fourth beam splitter, a polarization controller and an attenuator, and the chaotic laser source also comprises a first optical isolator;
The laser emitted by the distributed feedback laser is divided into two beams by the fourth beam splitter after passing through the optical fiber ring oscillator and the second optical circulator, one beam returns to the second optical circulator after passing through the attenuator and the polarization controller, and returns to the distributed feedback laser after passing through the second optical circulator and the optical fiber ring oscillator, so that the low-frequency energy is output to obtain lifted chaotic laser, and the chaotic laser is output after passing through the optical fiber ring oscillator, the fourth beam splitter and the first optical isolator.
The chaotic laser source further comprises a fifth beam splitter and a power meter, wherein the fifth beam splitter is arranged between the distributed feedback laser and the optical fiber ring oscillator, the input end of the fifth beam splitter is connected with the optical fiber ring oscillator, one output end of the fifth beam splitter is connected with the laser, the other output end of the fifth beam splitter is connected with the power meter, and the power meter is used for monitoring the light intensity of the returned distributed feedback laser.
The gain difference measurement type high-performance chaotic Brillouin sensing device further comprises an optical deflector and a second optical isolator, wherein the optical deflector and the second optical isolator are arranged between the erbium-doped optical fiber amplifier and the second beam splitter, the optical deflector is used for reducing the polarization sensitivity of the first chaotic laser, and the second optical isolator is used for isolating stray light output by one end of the sensing optical fiber.
The first beam splitter, the second beam splitter and the third beam splitter are X-fiber couplers, the output end of the chaotic laser source is connected with the input end of the first beam splitter through a single-mode fiber jumper, the first output end of the first beam splitter is connected with the input end of a single-sideband modulator through a single-mode fiber jumper, the output end of the single-sideband modulator is connected with the input end of an erbium-doped fiber amplifier through a single-mode fiber jumper, the output end of the erbium-doped fiber amplifier is connected with the input end of an optical scrambler through a single-mode fiber jumper, the output end of the optical scrambler is connected with the input end of a second optical isolator through a single-mode fiber jumper, the output end of the second optical isolator is connected with the input end of the second beam splitter through a single-mode fiber jumper, the first output end of the second beam splitter is connected with one end of a sensing fiber, and the second output end of the second beam splitter is connected with the input end of a second photoelectric detector through a single-mode fiber jumper;
The second output end of the first beam splitter is connected with the input end of the optical delay line through a single-mode fiber jumper, the output end of the optical delay line is connected with the input end of the semiconductor optical amplifier through a single-mode fiber jumper, the output end of the semiconductor optical amplifier is connected with the input end of the third beam splitter through a single-mode fiber jumper, the first output end of the third beam splitter is connected with the input end of the pulse optical amplifier through a single-mode fiber jumper, the output end of the pulse optical amplifier is connected with the first port of the first optical circulator through a single-mode fiber jumper, the second port of the first optical circulator is connected with the other end of the sensing optical fiber, the third port of the first optical circulator is connected with the input end of the first photoelectric detector through a single-mode fiber jumper, and the second output end of the third beam splitter is connected with the input end of the third photoelectric detector through a single-mode fiber jumper.
The sensing optical fiber adopts a G652 single mode optical fiber or a G655 single mode optical fiber.
In addition, the invention provides a gain difference measurement type high-performance chaotic Brillouin sensing method, which is realized by adopting the device and comprises the following steps:
s1, enabling the detection light and the pumping light to generate stimulated Brillouin amplification in a sensing optical fiber;
S2, carrying out cross-correlation operation on the transmission signal detected by the first photoelectric detector and the differential reference signal detected by the second photoelectric detector to obtain optical path difference of two paths of signals, carrying out optical path difference matching on the transmission signal and the differential reference signal, and carrying out differential operation on the transmission signal with the optical path difference matched and the differential reference signal to obtain chaotic Brillouin gain information;
S3, adjusting the optical path of the pump light through the optical delay line, so that stimulated Brillouin amplification of the probe light and the pump light occurs at different positions of the sensing optical fiber, and repeating the step S2, thereby acquiring event information along the whole sensing optical fiber.
Compared with the prior art, the invention has the following beneficial effects:
1. According to the method, the gain difference measurement is adopted to extract the chaotic Brillouin gain information, and the correlation algorithm is combined to realize the positioning of the correlation peak. Specifically, the invention utilizes the self-correlation characteristic of the chaotic signal with delta-like line type, carries out correlation operation through the transmission signal and the differential reference signal to obtain the time delay of the two paths of signals, and can accurately obtain the optical path difference of the two paths of signals according to the sampling rate of the data acquisition unit, thereby realizing the optical path matching of the two paths of signals and carrying out differential processing to obtain chaotic Brillouin gain information, and then carries out cross-correlation operation on the chaotic Brillouin gain information obtained by differential and the cross-correlation reference signal to realize the positioning of a correlation peak.
2. The invention provides a gain difference measurement type high-performance chaotic Brillouin sensing device and a gain difference measurement type high-performance chaotic Brillouin sensing method, which are based on the characteristics that the phase dynamic spectrum of chaotic laser is flat and the low-frequency energy is higher, the phase dynamic of the chaotic signal is converted into intensity fluctuation by utilizing the self-delay interference effect generated by an optical fiber ring oscillator, the low-frequency energy of the chaotic signal is greatly improved, and broadband chaotic laser with the lifted low-frequency energy is used as a light source, so that the energy distribution of the chaotic signal is more suitable for the low-frequency response characteristic of an electronic acquisition device and the low-frequency distribution characteristic of chaotic Brillouin gain information, the energy utilization efficiency of the chaotic signal is greatly improved, and the sensing performance of a chaotic BOCDA system is improved.
3. Compared with the existing phase modulation differential scheme (Journal of Lightwave Technology,2023,41 (1): 341-346), the invention ensures long-distance high spatial resolution and does not need to use an expensive phase modulator for phase modulation at the same time, thereby greatly reducing the experimental complexity and experimental cost. Compared with the existing detection path differential scheme (Optics Express,2018,26 (6): 6916-6928), the detection path differential scheme has the advantages that the sensing distance is remarkably improved, and polarization maintaining optical fibers are not needed, so that the detection path differential scheme has more excellent practicability.
4. Compared with the existing time domain differential high-speed chaotic Brillouin optical coherence domain monitoring scheme (Chinese patent application ZL202010454169. X), the method can effectively inhibit interference of chaotic intensity noise on gain information, improve signal-to-noise ratio of a system, and widen sensing distance while guaranteeing high spatial resolution.
Drawings
Fig. 1 is a schematic structural diagram of a gain differential measurement type high-performance chaotic brillouin sensing device according to a first embodiment of the present invention;
fig. 2 is a schematic structural diagram of a chaotic laser source according to a first embodiment of the present invention;
FIG. 3 is a spectrum diagram and a timing diagram of a chaotic laser with low-frequency energy lifting output by a chaotic laser source in an embodiment of the invention, and is compared with a traditional single-feedback chaotic laser;
fig. 4 is a diagram showing the chaotic brillouin gain information obtained by difference and the correlation peak distribution obtained by the cross correlation operation of the chaotic brillouin gain information and the pumping pulse signal in the embodiment of the present invention.
Fig. 5 is a schematic structural diagram of a gain differential measurement type high-performance chaotic brillouin sensing device according to a second embodiment of the present invention;
In the figure, a 1-chaotic laser source, a 2-first beam splitter, a 3-single sideband modulator, a 4-erbium-doped optical fiber amplifier, a 5-scrambler, a 6-second optical isolator, a 7-second beam splitter, an 8-broadband microwave signal source, a 9-optical delay line, a 10-semiconductor optical amplifier, an 11-third beam splitter, a 12-pulse optical amplifier, a 13-first optical circulator, a 14-sensing optical fiber, a 15-first photoelectric detector, a 16-second photoelectric detector, a 17-third photoelectric detector, an 18-data acquisition unit and a 19-computer are shown, wherein the 20-laser, the 21-fifth beam splitter, a 22-optical fiber ring oscillator, the 23-second optical circulator, the 24-fourth beam splitter, the 25-first optical isolator, a 26-power meter, a 27-polarization controller and a 28-attenuator are shown.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments, and all other embodiments obtained by persons of ordinary skill in the art without making creative efforts based on the embodiments of the present invention are all within the scope of protection of the present invention.
Example 1
As shown in FIG. 1, the first embodiment of the invention provides a gain differential measurement type high-performance chaotic Brillouin sensing device, which comprises a chaotic laser source 1, wherein chaotic laser output by the chaotic laser source 1 is divided into first chaotic laser and second chaotic laser through a first beam splitter 2, the first chaotic laser sequentially passes through a single-sideband modulator 3 and an erbium-doped optical fiber amplifier 4 and is divided into detection light and differential reference light through a second beam splitter 7, the detection light is incident to one end of a sensing optical fiber 14, the differential reference light is detected by a second photodetector 16, the second chaotic laser sequentially passes through an optical delay line 9 and a semiconductor optical amplifier 10 and is divided into pump light and cross-correlation reference light through a third beam splitter 11, the pump light is subjected to optical amplification through a pulse optical amplifier 12 and is injected from the other end of the sensing optical fiber 14 through a first optical fiber 13, the cross-correlation reference light is detected by the third optical fiber 17, the pump light and the detection light meet in the sensing optical fiber 14 and undergo stimulated Brillouin amplification, and a transmission signal in the sensing optical fiber 14 is output through the first optical fiber 13 and is detected by the first optical fiber 15.
The single sideband modulator 3 is used for modulating the first chaotic laser to generate frequency downshifting, and the downshifting amount is equal to the brillouin frequency shift amount in the sensing optical fiber 14; the erbium-doped optical fiber amplifier 4 is used for amplifying the first chaotic laser after frequency downshifting, the optical delay line 9 is used for adjusting the delay of the second chaotic laser, and the semiconductor optical amplifier 10 is used for modulating the continuous second chaotic laser into pulse chaotic light;
Specifically, the three detection signals are synchronously collected by the data collection unit 18 and sent to the computer 19 for data processing.
Specifically, in this embodiment, the specific method for performing data processing by the computer 19 is as follows:
Performing cross-correlation operation on the transmission signal detected by the first photoelectric detector 15 and the differential reference signal detected by the second photoelectric detector 16 to obtain an optical path difference of two paths of signals;
Then, carrying out optical path difference matching on the transmission signal and the differential reference signal, and carrying out differential operation on the transmission signal and the differential reference signal after the optical path difference matching to obtain chaotic Brillouin gain information;
And carrying out cross-correlation operation on the obtained chaotic Brillouin gain information and a cross-correlation reference signal detected by the third photoelectric detector 17 to realize the positioning of a correlation peak.
Specifically, in this embodiment, the first beam splitter 2, the second beam splitter 7, and the third beam splitter 11 are 1×2 optical fiber couplers, and the output end of the chaotic laser source 1 is connected to the input end of the first beam splitter 2 through a single mode fiber jumper, the first output end of the first beam splitter 2 is connected to the input end of the single sideband modulator 3 through a single mode fiber jumper, the output end of the single sideband modulator 3 is connected to the input end of the erbium-doped optical fiber amplifier 4 through a single mode fiber jumper, the output end of the erbium-doped optical fiber amplifier 4 is connected to the input end of the second beam splitter 7 through a single mode fiber jumper, the first output end of the second beam splitter 7 is connected to one end of the sensing optical fiber 14, and the second output end of the second beam splitter 7 is connected to the input end of the second photodetector 16 through a single mode fiber jumper;
The second output end of the first beam splitter 2 is connected with the input end of the optical delay line 9 through a single-mode fiber jumper, the output end of the optical delay line 9 is connected with the input end of the semiconductor optical amplifier 10 through a single-mode fiber jumper, the output end of the semiconductor optical amplifier 10 is connected with the input end of the third beam splitter 11 through a single-mode fiber jumper, the first output end of the third beam splitter 11 is connected with the input end of the pulse optical amplifier 12 through a single-mode fiber jumper, the output end of the pulse optical amplifier 12 is connected with the first port of the first optical circulator 13 through a single-mode fiber jumper, the second port of the first optical circulator 13 is connected with the other end of the sensing optical fiber 14, the third port is connected with the input end of the first photoelectric detector 15 through a single-mode fiber jumper, and the second output end of the third beam splitter 11 is connected with the input end of the third photoelectric detector 17 through a single-mode fiber jumper. In the first optical circulator 13, light input from the first port is output from the second port, and light input from the second port is output from the third port.
Further, in this embodiment, the chaotic laser source 1 is preferably a chaotic laser source with raised low-frequency energy, as shown in fig. 2, where the chaotic laser source 1 includes a laser 20, an optical fiber ring oscillator 22, and a feedback loop, where laser light emitted by the laser 20 is incident to the feedback loop through the optical fiber ring oscillator 22, and the feedback loop is used to feedback an incident laser part to the optical fiber ring oscillator 22 and the laser 20 in sequence, so that the laser 20 outputs the chaotic laser, and the chaotic laser output by the laser 20 is output after passing through the optical fiber ring oscillator 22 and the feedback loop, where the optical fiber ring oscillator 22 is used to raise the low-frequency energy in the chaotic laser output by the laser 20. Specifically, the laser 20 is a distributed feedback laser.
In this embodiment, based on the characteristics of flat phase dynamic spectrum and higher low-frequency energy of the chaotic laser, the optical fiber ring oscillator 22 is utilized to generate a self-delay interference effect, so that the phase dynamic of the chaotic signal is converted into intensity fluctuation, the low-frequency energy of the chaotic signal is greatly improved, and the obtained broadband chaotic laser with the low-frequency energy raised is used as a light source, so that the energy distribution of the chaotic signal is more suitable for the low-frequency response characteristic of an electronic acquisition device and the low-frequency distribution characteristic of chaotic Brillouin gain information, the energy utilization efficiency of the chaotic signal is greatly improved, and the sensing performance of a chaotic BOCDA system is improved.
Further, as shown in fig. 2, the feedback loop includes a second optical circulator 23, a fourth beam splitter 24, a polarization controller 27, and an attenuator 28, the chaotic laser source 1 further includes a first optical isolator 25, the laser light emitted by the distributed feedback laser 20 is split into two beams by the fourth beam splitter 24 after passing through the optical fiber ring oscillator 22 and the second optical circulator 23, one of the two beams is used as feedback light, after passing through the attenuator 28 and the polarization controller 27, and after passing through the second optical circulator 23 and the optical fiber ring oscillator 22, the feedback light returns to the distributed feedback laser 20, so that low-frequency energy is output to obtain elevated chaotic laser, and the chaotic laser is output after passing through the optical fiber ring oscillator 22, the fourth beam splitter 24 and the first optical isolator 25. The polarization controller 27 and the attenuator 28 can control the intensity and polarization of the feedback light, so that the laser 20 outputs the chaotic laser.
In addition, in this embodiment, the feedback loop may be another feedback loop for generating the chaotic laser device in the field, for example, the second optical circulator 23 may be replaced by a mirror disposed outside the polarization controller 27, and the light of the branch where the attenuator 28 and the polarization controller 27 are located may be returned to the laser 20 through the mirror, so as to output the chaotic laser.
Further, in this embodiment, the chaotic laser source 1 further includes a fifth beam splitter 21 and a power meter 26, wherein the fifth beam splitter 21 is disposed between the distributed feedback laser 20 and the fiber ring oscillator 22, an input end of the fifth beam splitter is connected to the fiber ring oscillator 22, an output end of the fifth beam splitter is connected to the laser 20, another output end of the fifth beam splitter is connected to the power meter 26, and the power meter 26 is used for monitoring the light intensity returned to the distributed feedback laser 20.
Specifically, in the present embodiment, the sensing fiber 14 adopts a G652 single-mode fiber or a G655 single-mode fiber. The semiconductor optical amplifier 10 is an OAM-SOA-PL type high extinction ratio semiconductor optical amplifier, and the data acquisition unit 18 is an oscilloscope. Specifically, in this embodiment, the wideband microwave signal source 8 is further included, and the wideband microwave signal source 8 is used to drive the single sideband modulator 3. The optical delay line 9 is a high-precision optical delay line. The optical delay line used in this example had a delay range of 168mm, a delay accuracy of 0.3 μm and a delay step of 0.001mm.
Specifically, the working principle of the gain differential measurement type high-performance chaotic brillouin sensing device of the embodiment is as follows:
1. The chaotic laser source 1 outputs broadband chaotic laser with the wavelength of 1550nm, the center frequency of 0 and the low-frequency energy of which is obviously improved. As shown in fig. 3, the frequency spectrum diagram and the time sequence diagram of the broadband chaotic laser with the low-frequency energy being obviously increased and the traditional chaotic laser are shown. The output signal of the light source is divided into a first chaotic laser and a second chaotic laser by a first beam splitter 2 formed by a 10:90 1×2 optical fiber coupler.
2. The first chaotic laser (90%) is modulated by a single sideband modulator 3, the frequency of an original signal is shifted downwards, the frequency of an output signal is v 0-vB, v B is the Brillouin frequency shift, and the value of the first chaotic laser is 11GHz for a common quartz single mode fiber. The single sideband modulator 3 is driven by a broadband microwave signal source 8 which outputs a sinusoidal signal having a frequency range of 9khz to 13ghz and an amplitude range of-20 to 2 dbm. The modulated optical signal is amplified using an erbium doped fiber amplifier 4 to compensate for the optical power loss due to the modulation. The amplified optical signal is split into two paths by the second beam splitter 7 formed by the 1×2 optical fiber coupler of 20:80, the output of the first output end (80%) of the second beam splitter 7 is used as detection light to be incident into the sensing optical fiber 14, and the output of the second output end (20%) of the second beam splitter 7 is used as differential reference light to be converted into an electric signal by the second photoelectric detector 16 and is input into the data acquisition unit 18 by a high-frequency coaxial cable for real-time signal acquisition.
3. The second chaotic laser (10%) of the other path is subjected to pulse modulation by an OAM-SOA-PL type high extinction ratio semiconductor optical amplifier 10 after passing through a high-precision optical delay line 9, and the modulation aims to prevent non-peak amplification outside a central correlation peak and noise accumulation along an optical fiber and improve the sensing distance of the system. Then, the third beam splitter 11 formed by the 1×2 optical fiber coupler of 10:90 is split into two beams, one beam output by the first output end (90%) is used as pump light, the pump light is amplified by the pulse light amplifier 12, and then is incident into the sensing optical fiber 14 by the first optical circulator 13, meets the probe light in the sensing optical fiber 14, and generates stimulated brillouin scattering. A beam output by the second output end (10%) is used as cross-correlation reference light, converted into an electric signal by the third photodetector 17 and input into the data acquisition unit 18 by a high-frequency coaxial cable for real-time signal acquisition.
4. The probe light and the pump light transmitted in opposite directions meet at a certain position in the sensing optical fiber 14 to generate a correlation peak, and the stimulated brillouin amplification is limited to the correlation peak. The transmission signal output by the third port of the first optical circulator 13 is converted into an electrical signal by the first photodetector 15 and is input into the data acquisition unit 18 by a high-frequency coaxial cable for real-time signal acquisition.
5. The time delay of the two signals is obtained by performing correlation operation on the transmission signal and the differential reference signal, and the optical path difference of the two signals can be accurately obtained according to the sampling rate of the data acquisition unit 18.
Because the chaotic Brillouin gain information is weak, the influence of the chaotic Brillouin gain information when the optical path difference is matched is ignored. Let the transmission signal x 1 (t) be denoted as x 1 (t) =s (t), the differential reference signal x 2 (t) be denoted as x 2(t)＝s(t+Dc), where D c is the delay of two signals, and the cross correlation coefficient of the transmission signal x 1 (t) and the differential reference signal x 2 (t) is:
Rx1x2＝E[s(t)s(t+Dc+τ1)]＝Rss(τ1+Dc); (1)
Wherein, R x1x2 represents the cross-correlation coefficient of the two paths of signals of the transmission signal and the differential reference signal, E represents the cross-correlation operation, R ss(τ1+Dc) represents the first cross-correlation function, τ 1 represents the cross-correlation independent variable, R ss(τ1+Dc) also takes the maximum value when the cross-correlation function of the transmission signal x 1 (t) and the differential reference signal x 2 (t) takes the maximum value, and because of R ss(τ1+Dc)≤Rss (0), the cross-correlation independent variable τ 1 when the cross-correlation function takes the maximum value is the time delay D c. The time delay information is obtained through cross correlation, and then the optical path difference of two paths of signals can be accurately obtained according to the sampling rate of the data acquisition unit.
By using the obtained time delay information, the chaotic light information sent by the light source at the same time can be correspondingly arranged in two groups of time sequences, and then differential processing is carried out. The optical path difference between the two paths is eliminated.
6. As shown in fig. 4 (a), the difference processing is performed on the two paths of signals of the transmission signal and the differential reference signal, which is the result of performing the difference between the transmission signal and the differential reference signal through the obtained time delay D c, so that the interference of the chaotic intensity noise on the gain information is effectively suppressed, and the chaotic brillouin gain information is obtained.
P(t)=Pprobe(t)+Pgain(t); (2)
Where P (t) represents the power of the transmission signal, P probe (t) represents the transmission power of the probe light, and P gain (t) represents the power of the chaotic brillouin gain information. And obtaining weak chaotic Brillouin gain information through differential processing.
7. The correlation operation is performed by the chaotic brillouin gain information and the cross-correlation reference signal, as shown in (b) of fig. 4, which is the result of cross-correlation between the chaotic brillouin gain information and the cross-correlation reference signal, and the positioning of the correlation peak can be realized according to the cross-correlation result.
Let the brillouin gain signal x 3 (t) be denoted as x 3 (t) =h (t), the cross-correlation reference signal x 4 (t) be denoted as x 4(t)＝h(t+Dx), where D x is the delay of two signals, and the cross-correlation coefficient of the transmission signal x 3 (t) and the differential reference path x 4 (t) is:
Rx3x4＝E[h(t)h(t+Dx+τ2)]＝Rhh(τ2+Dx); (3)
Wherein, R x3x4 represents the cross-correlation coefficient of the two signals, E represents the cross-correlation operation, R hh(τ2+Dx) represents the second cross-correlation function, τ 2 represents the autocorrelation variable, R hh(τ2+Dx) also takes the maximum value when the cross-correlation function of the chaotic brillouin gain signal x 3 (t) and the cross-correlation reference signal x 4 (t) takes the maximum value, and τ 2 when the second cross-correlation function R hh(τ2+Dx takes the maximum value is the time delay D x because of R hh(τ2+Dx)≤Rhh (0). Therefore, through carrying out cross-correlation operation on the two paths of signals, the value of the time delay D x corresponding to the correlation peak of the cross-correlation function is determined, and the accurate positioning of the correlation peak can be realized.
Example two
As shown in fig. 5, a second embodiment of the present invention provides a gain difference measurement type high performance chaotic brillouin sensing device, which comprises a chaotic laser source 1, a first beam splitter 2, a single-side band modulator 3, an erbium-doped fiber amplifier 4, a second beam splitter 7, an optical delay line 9, a semiconductor optical amplifier 10, a third beam splitter 11, a pulse optical amplifier 12, a first optical circulator 13, the sensing optical fiber 14, a first photodetector 15, a second photodetector 16, a third photodetector 17, a data acquisition unit 18 and a computer 19, as in the first embodiment, and further comprises an optical scrambler 5 and a second optical isolator 6, wherein the optical scrambler 5 and the second optical isolator 6 are arranged between one ends of the erbium-doped fiber amplifier 4 and the second beam splitter 7, the optical scrambler 5 is used for reducing polarization sensitivity of the first chaotic laser, suppressing gain fluctuation caused by polarization, and the second optical isolator 6 is used for isolating one end of the output of the sensor 14 from the erbium-doped fiber amplifier 4.
In this embodiment, the chaotic laser output by the chaotic laser source 1 is divided into a first chaotic laser and a second chaotic laser by the first beam splitter 2, the first chaotic laser sequentially passes through the single-sideband modulator 3, the erbium-doped optical fiber amplifier 4, the optical scrambler 5 and the second optical isolator 6, then is divided into detection light and differential reference light by the second beam splitter 7, the detection light is incident to one end of the sensing optical fiber 14, the differential reference light is detected by the second optical detector 16, the second chaotic laser sequentially passes through the optical delay line 9 and the semiconductor optical amplifier 10, and then is divided into pump light and cross-correlation reference light by the third beam splitter 11, after the pump light is amplified by the pulse optical amplifier 12, the pump light is injected from the other end of the sensing optical fiber 14 by the first optical circulator 13, the cross-correlation reference light is detected by the third optical detector 17, and the transmission signal in the sensing optical fiber 14 is output by the first optical circulator 13 and then is detected by the first optical detector 15. The single-sideband modulator 3 is used for modulating the first chaotic laser to generate frequency downshifting, the downshifting amount is equal to the Brillouin frequency shift amount in the sensing optical fiber 14, the erbium-doped fiber amplifier 4 is used for amplifying the first chaotic laser after the frequency downshifting, the optical delay line 9 is used for adjusting the delay of the second chaotic laser, and the semiconductor optical amplifier 10 is used for modulating the continuous second chaotic laser into pulse chaotic light.
Example III
The third embodiment of the invention provides a gain difference measurement type high-performance chaotic Brillouin sensing method, which is realized by adopting the device in the first or second embodiment, and comprises the following steps:
s1, enabling the detection light and the pumping light to generate stimulated Brillouin amplification in a sensing optical fiber;
S2, carrying out cross-correlation operation on the transmission signal detected by the first photoelectric detector 15 and the differential reference signal detected by the second photoelectric detector 16 to obtain optical path difference of two paths of signals, carrying out optical path difference matching on the transmission signal and the differential reference signal, and carrying out differential operation on the transmission signal with the optical path difference matched and the differential reference signal to obtain chaotic Brillouin gain information;
s3, adjusting the optical path of the pump light through the optical delay line 9, so that stimulated Brillouin amplification of the probe light and the pump light occurs at different positions of the sensing optical fiber, and repeating the step S2, thereby acquiring event information along the whole sensing optical fiber.
It should be noted that the above embodiments are merely for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that the technical solution described in the above embodiments may be modified or some or all of the technical features may be equivalently replaced, and these modifications or substitutions do not make the essence of the corresponding technical solution deviate from the scope of the technical solution of the embodiments of the present invention.
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