CN113091783A - High-sensitivity sensing device and method based on two-stage Brillouin scattering - Google Patents
High-sensitivity sensing device and method based on two-stage Brillouin scattering Download PDFInfo
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- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
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- G01D5/35338—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using other arrangements than interferometer arrangements
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Abstract
本发明属于分布式光纤传感技术领域，公开了一种基于二级布里渊散射的高灵敏传感装置及方法，方法包括以下步骤：将同一激光器输出的窄线宽激光信号分为两路；一路光信号作为参考光信号，第二路光信号作为传感光；使参考光进入参考光纤并发生自发布里渊散射，将产生的布里渊后向散射参考光重新反向输入参考光纤中使其再次发生布里渊散射并输出二级布里渊后向散射参考光；另一路作为传感光，将传感光调制成为脉冲光后，进入传感光纤，将产生的布里渊后向散射传感光通过第二调制器重新进行脉冲调制后再次反向输入传感光纤并输出二级布里渊后向散射传感光；采集并分析拍频信号，解调传感光纤中的温度/应变信息。本发明可有效提高系统的测量精度。
The invention belongs to the technical field of distributed optical fiber sensing, and discloses a high-sensitivity sensing device and method based on secondary Brillouin scattering. The method includes the following steps: dividing a narrow linewidth laser signal output by the same laser into two paths ; One optical signal is used as the reference optical signal, and the second optical signal is used as the sensing light; the reference light enters the reference fiber and spontaneous Brillouin scattering occurs, and the generated Brillouin backscattered reference light is reversely input into the reference fiber Make it Brillouin scattering again and output secondary Brillouin backscattering reference light; the other way is used as sensing light, after modulating the sensing light into pulse light, it enters the sensing fiber, and the generated Brillouin backscattering The sensing light is re-pulsed by the second modulator and then reversely input to the sensing fiber and outputs the second-level Brillouin backscattered sensing light; the beat frequency signal is collected and analyzed, and the temperature/strain information in the sensing fiber is demodulated . The invention can effectively improve the measurement precision of the system.
Description
Technical Field
The invention belongs to the technical field of distributed optical fiber sensing systems, and particularly relates to a high-sensitivity sensing device and method based on two-stage Brillouin scattering.
Background
Compared with the traditional sensing system, the distributed optical fiber sensing has the advantages of light weight, corrosion resistance, electromagnetic interference resistance and the like, and the optical fiber can be used as a sensor and a signal transmission medium to realize continuous and long-distance sensing. The sensing network composed of the optical fibers can realize large-area sensing measurement. The method has obvious advantages in the aspect of structural health monitoring of oil pipelines and large buildings. The distributed optical fiber sensing technology based on Brillouin scattering can realize high-precision temperature and strain measurement by utilizing the linear relation between Brillouin frequency shift and temperature and strain. Currently, optical fiber sensing systems using brillouin scattering include Brillouin Optical Time Domain Reflectometry (BOTDR), Brillouin Optical Time Domain Analysis (BOTDA), Brillouin Optical Frequency Domain Analysis (BOFDA), and Brillouin Optical Correlation Domain Analysis (BOCDA).
In the aspect of improving the measurement precision of Brillouin frequency shift quantity by the Brillouin optical time domain reflection technology, researchers provide a method for improving the measurement precision of frequency sweep BOTDR (FS-BOTDR) based on light source line width optimization. Research shows that the FS-BOTDR measurement accuracy is improved along with the narrowing of the line width of a light source in a certain range, see: white spirit, BOTDR system performance improvement key technology research [ D ]. Shanxi, Taiyuan university of technology, 2019; however, when the line width is too narrow, coherent rayleigh noise is aggravated, so that the Brillouin Frequency Shift (BFS) measurement accuracy is reduced. Furthermore, it has been found that the optimum line width can be determined by comparing BFS accuracy at different line widths. In the Brillouin optical time domain analysis technology, a differential pulse width pair method (Xiaoyi Bao and Liang Chen. Recent Progress in Brillouin Scattering Based Fiber Sensors [ J ]. Sensors, 2011, 11: 4152 4187) is adopted to achieve a spatial resolution of 2cm and a temperature resolution of 2 ℃ at a sensing distance of 2km, and by utilizing gain and loss effect cascade in a stimulated Brillouin Scattering process (jin Qian. Brillouin Brillouin high-precision distributed optical Fiber sensing system, optimization and realization of [ D ]. Shanghai: Shanghai transportation university, 2013.), the Brillouin optical correlation domain analysis is carried out to improve the Brillouin net gain.
The existing Brillouin sensing technology is all based on a first-stage Brillouin scattering sensing device, and due to the characteristics of the first-stage Brillouin scattering, the method can improve the measurement accuracy of measurement by using Brillouin frequency shift amount, but is limited by the sensitivity of a first-stage Brillouin scattering signal, and the measurement accuracy is difficult to meet higher requirements.
Disclosure of Invention
The invention overcomes the defects of the prior art, and solves the technical problems that: the high-sensitivity sensing device based on the two-stage Brillouin scattering is used for improving the measurement precision of the Brillouin frequency shift quantity and further improving the performance of the whole system.
In order to solve the technical problems, the invention adopts the technical scheme that: a high-sensitivity sensing method based on two-stage Brillouin scattering comprises the following steps:
s1, dividing narrow linewidth laser signals output by the same laser into two paths;
s2, one path of optical signal is used as a reference optical signal, and the second path of optical signal is used as sensing light; enabling the reference light to enter the reference optical fiber and generate spontaneous Brillouin scattering in the reference optical fiber, inputting the generated Brillouin backscattering reference light into the reference optical fiber again in a backward mode to enable the reference optical fiber to generate Brillouin scattering again, and outputting the generated second-stage Brillouin backscattering reference light; the other path of signal is used as sensing light, after the sensing light is modulated into pulse light by the first modulator, the pulse sensing light enters the sensing optical fiber and generates spontaneous Brillouin scattering in the sensing optical fiber, the generated Brillouin backscattering sensing light is re-pulse-modulated by the second modulator and then is reversely input into the sensing optical fiber again to generate Brillouin scattering again, and the generated secondary spontaneous Brillouin backscattering sensing light is output;
and S3, performing beat frequency on the second-level Brillouin backscattering reference light and the second-level spontaneous Brillouin backscattering sensing light output in the step S2, collecting and analyzing beat frequency signals, and demodulating temperature/strain information in the sensing optical fiber.
The high-sensitivity sensing method based on the two-stage Brillouin scattering further comprises the following steps of:
and changing the delay time tau of the first modulator and the second modulator to realize the measurement of any point in the sensing optical fiber.
The high-sensitivity sensing method based on the two-stage Brillouin scattering further comprises the following steps of:
and scanning the delay time tau of the first modulator and the second modulator to realize real-time monitoring of the sensing optical fiber along the line.
In step S3, the specific method for demodulating the temperature/strain information in the sensing optical fiber is as follows:
and analyzing the beat frequency signal to obtain a second-stage Brillouin frequency shift quantity, and demodulating temperature/strain information through the second-stage Brillouin frequency shift quantity.
The invention also provides a high-sensitivity sensing device based on the two-stage Brillouin scattering, which comprises: the output end of the narrow linewidth laser is connected with the optical splitter;
the first output end of the optical splitter is connected with the first port of the first optical circulator, the second port of the first optical circulator is connected with one end of the reference optical fiber, and the third port is connected with the first port of the second optical circulator; the second port of the second optical circulator is connected with the other end of the reference optical fiber, and the third port is connected with the first input end of the optical coupler;
the second output end of the optical splitter is connected with the first port of the third circulator through the first modulator, the second port of the third circulator is connected with one end of the sensing optical fiber, and the third port is connected with the first port of the fourth optical circulator through the second modulator; a second port of the fourth optical circulator is connected with the other end of the sensing optical fiber, and a third port of the fourth optical circulator is connected with a second input end of the optical coupler;
the output end of the pulse generator is connected with the control ends of the first modulator and the second modulator and is used for driving the first modulator and the second modulator and controlling the relative delay time tau of the first modulator and the second modulator;
the output end of the coupler is connected with a photoelectric detector, the photoelectric detector is used for receiving beat frequency signals of second-level Brillouin spontaneous scattering signals generated in the sensing optical fiber and the reference optical fiber, and the output end of the photoelectric detector is connected with a spectrum analyzer; the spectrum analyzer is used for collecting and analyzing beat frequency signals and demodulating temperature/strain information in the sensing optical fiber.
The high-sensitivity sensing device based on the two-stage Brillouin scattering further comprises a first erbium-doped fiber amplifier, wherein the first erbium-doped fiber amplifier is arranged between the narrow linewidth laser and the optical splitter and used for amplifying an output signal of the narrow linewidth laser.
The high-sensitivity sensing device based on two-stage Brillouin scattering further comprises a first optical filter and a second optical filter, wherein the first optical filter is arranged between the third port of the first optical circulator and the first port of the second optical circulator and is used for filtering stray signals in Brillouin backscattering reference light; and the second optical filter is arranged between the third port of the second optical circulator and the first port of the fourth optical circulator and is used for filtering stray signals in the Brillouin backscattering sensing light.
The high-sensitivity sensing device based on the two-stage Brillouin scattering further comprises a second erbium-doped fiber amplifier and a pulse light amplifier;
the second erbium-doped fiber amplifier is arranged between the first optical filter and the first port of the second optical circulator, and the pulse optical amplifier is arranged between the second optical filter and the first port of the fourth optical circulator.
The optical splitter is a 1 x 2 optical fiber coupler.
The first and second modulators are electro-optic intensity modulators.
Compared with the prior art, the invention has the following beneficial effects:
1. compared with the existing optical fiber sensing system based on the primary Brillouin scattering, the temperature/strain measuring device based on the secondary Brillouin scattering has the characteristic that the temperature/strain demodulated through the secondary Brillouin frequency shift is 2 times of temperature/strain sensitivity, and the temperature measurement is carried out by applying the secondary Brillouin frequency shift coefficient, so that the measurement precision of the system can be effectively improved.
2. The invention utilizes the time delay tau of two electro-optical intensity modulators to realize the measurement of any position of the sensing optical fiber. The sensing measurement of any position to be measured of the sensing optical fiber can be realized by adjusting the time delay tau of the two electro-optic intensity modulators, and in addition, the real-time monitoring of the sensing optical fiber along the line can be realized by scanning the time delay tau with a specific step length.
Drawings
Fig. 1 is a schematic structural diagram of a high-sensitivity temperature/strain sensing device based on two-stage brillouin scattering according to an embodiment of the present invention.
In fig. 1: the optical fiber laser comprises a 1-narrow line width laser, a 2-first erbium-doped optical fiber amplifier, a 3-optical splitter, a 4-first optical circulator, a 5-first optical filter, a 6-reference optical fiber, a 7-second erbium-doped optical fiber amplifier, an 8-second optical circulator, a 9-optical coupler, a 10-photoelectric detector, a 11-spectrum analyzer, a 12-pulse generator, a 13-first modulator, a 14-third optical circulator, a 15-second optical filter, a 16-sensing optical fiber, a 17-second modulator, an 18-pulse optical amplifier and a 19-fourth optical circulator.
Fig. 2 is a frequency domain schematic diagram of the implementation of the method of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments; all other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example one
As shown in fig. 1, a first embodiment of the present invention provides a high-sensitivity sensing device based on two-stage brillouin scattering, including: the device comprises a narrow-linewidth laser 1, a first erbium-doped fiber amplifier 2, an optical splitter 3, a first optical circulator 4, a first optical filter 5-, a reference fiber 6, a second erbium-doped fiber amplifier 7, a second optical circulator 8, an optical coupler 9, a photoelectric detector 10, a spectrum analyzer 11, a pulse generator 12, a first modulator 13, a third optical circulator 14, a second optical filter 15, a sensing fiber 16, a second modulator 17, a pulsed light amplifier 18 and a fourth optical circulator 19.
The output end of the narrow linewidth laser 1 is connected with the optical splitter 3, the first output end of the optical splitter 3 is connected with the first port of the first optical circulator 4, the second port of the first optical circulator 4 is connected with one end of the reference optical fiber 6, and the third port is connected with the first port of the second optical circulator 8; a second port of the second optical circulator 8 is connected with the other end of the reference optical fiber 6, and a third port is connected with a first input end of the optical coupler 9; the second output end of the optical splitter 3 is connected with the first port of a third circulator 14 through a first modulator 13, the second port of the third circulator 14 is connected with one end of a sensing optical fiber 16, and the third port is connected with the first port of a fourth optical circulator 19 through the second modulator 13; a second port of the fourth optical circulator 19 is connected with the other end of the sensing optical fiber 16, and a third port is connected with a second input end of the optical coupler 9; the output terminal of the pulse generator 12 is connected to the control terminals of the first modulator 13 and the second modulator 17, and is used for driving the first modulator 13 and the second modulator 17 and controlling the relative delay time τ thereof. The output end of the coupler 9 is connected with a photoelectric detector 10, and the output end of the photoelectric detector 10 is connected with a spectrum analyzer 11; the spectrum analyzer 11 is used for collecting and analyzing beat frequency signals and demodulating temperature/strain information in the sensing optical fiber.
Further, the high-sensitivity sensing device based on two-stage brillouin scattering of the present embodiment further includes a first erbium-doped fiber amplifier 2, where the first erbium-doped fiber amplifier 2 is disposed between the narrow linewidth laser 1 and the optical splitter 3, and is configured to amplify an output signal of the narrow linewidth laser 1.
Further, the high-sensitivity sensing device based on two-stage brillouin scattering of this embodiment further includes a first optical filter 5 and a second optical filter 15, where the first optical filter 5 is disposed between the third port of the first optical circulator 4 and the first port of the second optical circulator 8, and is used to filter a stray signal in the reference light of brillouin backscattering; the second optical filter 15 is disposed between the third port of the second optical circulator 14 and the first port of the fourth optical circulator 19, and is configured to filter a stray signal in the brillouin backscatter sensing light.
Further, the high-sensitivity sensing device based on the two-stage brillouin scattering of the present embodiment further includes a second erbium-doped fiber amplifier 7 and a pulsed light amplifier 18; the second erbium-doped fiber amplifier 7 is disposed between the first optical filter 5 and the first port of the second optical circulator 8, and the pulsed optical amplifier 18 is disposed between the second optical filter 15 and the first port of the fourth optical circulator 19.
Specifically, in this embodiment, the optical splitter 3 is a 1 × 2 fiber coupler. The first modulator 13 and the second modulator 17 are electro-optical intensity modulators.
Specifically, in this embodiment, the devices are connected by single-mode fiber jumpers, for example, the narrow-linewidth laser 1, the first erbium-doped fiber amplifier 2, the optical splitter 3, and the first optical circulator 4 are connected by single-mode fiber jumpers, the first optical circulator 4, the first optical filter 5, the second erbium-doped fiber amplifier 7, and the second optical circulator 8 are connected by single-mode fiber jumpers, and the optical splitter 3, the first modulator 13, the third optical circulator 14, the second optical filter 15, the second modulator 17, the pulsed light amplifier 18, and the fourth optical circulator 19 are connected by single-mode fiber jumpers. The second optical circulator 8 and the fourth optical circulator 19 are connected to the optical coupler 9 by a single-mode optical fiber jumper.
In this embodiment, the narrow linewidth laser source signal emitted from the narrow linewidth laser 1Firstly, the mixed light is amplified by a first erbium-doped fiber amplifier 2; the amplified laser signal is divided into two paths by the optical splitter 3; the first path of optical signal is used as a reference optical signal, and the second path of optical signal is used as sensing light; frequency v0The reference light enters a reference optical fiber 6 through a first optical circulator 4, spontaneous Brillouin scattering occurs in the reference optical fiber 6, and backward scattering light after the spontaneous Brillouin scattering has a frequency v relative to the reference lightB refFrequency shift of which the frequency becomes v0-vB ref(ii) a The backscattered light at this time is called brillouin backscattered reference light, the brillouin backscattered reference light sequentially enters the first optical filter 5 and the second erbium-doped fiber amplifier 7 through the first optical circulator 4, reversely enters the reference fiber 6 through the second optical circulator 8 again, spontaneous brillouin scattering occurs again in the reference fiber 6, the generated spontaneous brillouin backscattered light is called second-order brillouin backscattered reference light, and the frequency is v0-vB ref- vB1 refThe second-order brillouin backscattered reference light enters the optical coupler 9 after passing through the second optical circulator 8.
After the sensing light passes through the first modulator 13 (electro-optical intensity modulator), a signal emitted from the first channel of the pulse generator 12 is applied to the first modulator 13; the pulse light obtained after modulation by the first modulator 13 enters the sensing optical fiber 16 through the third optical circulator 14; after brillouin scattering occurs at a point х in the photosensitive fiber 16, the obtained backward spontaneous brillouin scattered light (continuous light) enters through the second port of the third optical circulator 14, exits through the third port thereof, and is filtered by the second optical filter 15 to obtain a frequency v0-vBEnters a second modulator 17 (electro-optical intensity modulator), and the signal emitted by the second channel of the pulse generator 12 is applied to the second modulator 17; there is a delay of time τ with respect to the first modulator 13 to enable measurement at any point of the sensing fiber 16. The specific implementation method is that the delay time tau = 2 х/v, wherein x represents the position of the measurement point corresponding to the delay, v represents the propagation speed of the light in the optical fiber, and the frequency coming out of the second modulator 17 is v0-vBThe pulse light is amplified by the pulse light amplifier 18 and enters the sensing optical fiber 16 through the fourth optical circulator 19, and the frequency of the backscattered light after spontaneous Brillouin scattering is v0-vB-vB1The two-stage spontaneous brillouin backscatter sensing light enters the optical fiber coupler 9 through the fourth optical circulator 19, performs beat frequency with a reference light signal, detects the obtained beat frequency signal through the photoelectric detector 10, and finally accesses the obtained electric signal to the spectrum analyzer 11.
Wherein, vB ref Representing a first order Brillouin frequency shift, v, of a reference pathB1 refRepresenting a second order brillouin frequency shift of the reference path; v isBRepresenting a first order Brillouin frequency shift, v, of a sensing pathB1 Representing a second order brillouin frequency shift of the sensing path.
In this embodiment, the narrow bandwidth laser source frequency in the system is v0Generating a frequency v0The reference light and the sensing light are not subjected to temperature/strain change, and if the temperature of the sensing optical fiber changes, the generated Brillouin frequency shift amount of the sensing optical fiber changes. The optical frequency of backward Stokes scattering generated by spontaneous Brillouin scattering of the reference light for the first time is v0-vB refThe backward Stokes scattering light frequency generated by the second spontaneous Brillouin scattering is v0-vB ref- vB1 ref(ii) a The optical frequency of backward Stokes scattering generated by the first spontaneous Brillouin scattering of the photosensitive body is v0-vBThe backward Stokes scattering light frequency generated by the second spontaneous Brillouin scattering is v0-vB-vB1See fig. 2. And finally, performing beat frequency on the reference light and the sensing light to obtain a second-stage Brillouin frequency shift at the temperature/strain change zone. The obtained two-stage Brillouin frequency shift amount corresponds to a specific temperature/strain variation amount, so that the temperature/strain can be demodulated to perform distributed sensing.
Specifically, taking temperature sensing as an example, incident light generates a signal in the sensing fiberThe optical frequency after stage Brillouin scattering is v0-vBThe optical frequency after the second-order Brillouin scattering is v0-vB-vB1The amount of frequency shift after the occurrence of the second order Brillouin scattering is therefore vB+vB1. By sensing beat frequency of light and reference light, frequency difference v between two beams can be obtainedB+vB1-（vB ref- vB1 ref) Has a value of (v) a frequency shift amount of the reference lightB ref- vB1 refIt is known that the frequency shift amount v after the second-order Brillouin scattering is calculatedB+vB1. Defining the temperature sensitivity coefficient as:
CT= （vB+vB1）/∆T； （1）
wherein, CTAnd the temperature sensitivity coefficient is expressed, the unit of the temperature sensitivity coefficient is MHz/DEG C, T is the temperature variation, and the corresponding relation between the second-level Brillouin scattering frequency shift quantity and the temperature can be established through the temperature sensitivity coefficient. The calibration method of the temperature sensitivity coefficient can measure the frequency shift v of the corresponding second-stage Brillouin scattering by adjusting the temperature of the sensing optical fiberB+vB1And then can be obtained by calculation through the formula (1). The strain demodulation can also be performed by the same method as described above.
In this example, the second order brillouin scattering is achieved at any position of the sensing fiber by controlling the time interval τ between the first modulator 13 and the second modulator 17. The specific implementation manner is that when measuring the second-order brillouin frequency shift of the temperature change region of the sensing fiber 16, the scattered light at the position where the first-order brillouin scattering occurs needs to be used as the pump light of the second-order brillouin scattering, and finally the temperature/strain measurement is realized by demodulating the measured brillouin frequency shift of the second-order brillouin scattering. In order to make the light modulated by the second modulator 17 the scattered light after the first-order brillouin scattering occurs, a time delay τ needs to be added between the first modulator 13 and the first modulator 13. The specific magnitude of τ is determined by the distance of the temperature/strain change region from the incident end of the fiber.
Example two
The embodiment of the invention provides a high-sensitivity sensing method based on two-stage Brillouin scattering, which comprises the following steps of:
s1, dividing narrow linewidth laser signals output by the same laser into two paths;
s2, one path of optical signal is used as a reference optical signal, and the second path of optical signal is used as sensing light; enabling the reference light to enter the reference optical fiber and generate spontaneous Brillouin scattering in the reference optical fiber, inputting the generated Brillouin backscattering reference light into the reference optical fiber again in a backward mode to enable the reference optical fiber to generate Brillouin scattering again, and outputting the generated second-stage Brillouin backscattering reference light; the other path of signal is used as sensing light, after the sensing light is modulated into pulse light by the first modulator, the pulse sensing light enters the sensing optical fiber and generates spontaneous Brillouin scattering in the sensing optical fiber, the generated Brillouin backscattering sensing light is re-pulse-modulated by the second modulator and then is reversely input into the sensing optical fiber again to generate Brillouin scattering again, and the generated secondary spontaneous Brillouin backscattering sensing light is output;
and S3, performing beat frequency on the second-level Brillouin backscattering reference light and the second-level spontaneous Brillouin backscattering sensing light output in the step S2, collecting and analyzing beat frequency signals, and demodulating temperature/strain information in the sensing optical fiber.
Specifically, the high-sensitivity sensing method based on the two-stage brillouin scattering of the embodiment further includes the following steps:
and changing the delay time tau of the first modulator and the second modulator to realize the measurement of any point in the sensing optical fiber.
Specifically, the high-sensitivity sensing method based on the two-stage brillouin scattering of the embodiment further includes the following steps: and scanning the delay time tau of the first modulator and the second modulator to realize real-time monitoring of the sensing optical fiber along the line.
Specifically, in step S3, the specific method for demodulating the temperature/strain information in the sensing optical fiber is as follows: and analyzing the beat frequency signal to obtain a second-stage Brillouin frequency shift quantity, and demodulating temperature/strain information through the second-stage Brillouin frequency shift quantity.
In summary, the invention provides a device and a method for measuring temperature/strain based on two-stage brillouin scattering, and temperature/strain sensitivity coefficient is 2 times that of temperature/strain through two-stage brillouin frequency shift demodulation, so that measurement accuracy of a system can be effectively improved. In addition, the invention utilizes the time delay tau of two electro-optical intensity modulators to realize the measurement of any position of the sensing optical fiber. The sensing measurement of any position to be measured of the sensing optical fiber can be realized by adjusting the time delay tau of the two electro-optic intensity modulators, and the real-time monitoring of the sensing optical fiber along the line can be realized by scanning the time delay tau with a specific step length.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (10)
1. A high-sensitivity sensing method based on two-stage Brillouin scattering is characterized by comprising the following steps:
s1, dividing narrow linewidth laser signals output by the same laser into two paths;
s2, one path of optical signal is used as a reference optical signal, and the second path of optical signal is used as sensing light; enabling the reference light to enter the reference optical fiber and generate spontaneous Brillouin scattering in the reference optical fiber, inputting the generated Brillouin backscattering reference light into the reference optical fiber again in a backward mode to enable the reference optical fiber to generate Brillouin scattering again, and outputting the generated second-stage Brillouin backscattering reference light; the other path of signal is used as sensing light, after the sensing light is modulated into pulse light by the first modulator, the pulse sensing light enters the sensing optical fiber and generates spontaneous Brillouin scattering in the sensing optical fiber, the generated Brillouin backscattering sensing light is re-pulse-modulated by the second modulator and then is reversely input into the sensing optical fiber again to generate Brillouin scattering again, and the generated secondary spontaneous Brillouin backscattering sensing light is output;
and S3, performing beat frequency on the second-level Brillouin backscattering reference light and the second-level spontaneous Brillouin backscattering sensing light output in the step S2, collecting and analyzing beat frequency signals, and demodulating temperature/strain information in the sensing optical fiber.
2. The two-stage brillouin scattering-based high-sensitivity sensing method according to claim 1, further comprising the steps of:
and changing the delay time tau of the first modulator and the second modulator to realize the measurement of any point in the sensing optical fiber.
3. The two-stage brillouin scattering-based high-sensitivity sensing method according to claim 1, further comprising the steps of:
and scanning the delay time tau of the first modulator and the second modulator to realize real-time monitoring of the sensing optical fiber along the line.
4. The method for sensing high sensitivity based on two-stage brillouin scattering according to claim 1, wherein in step S3, the specific method for demodulating the temperature/strain information in the sensing optical fiber is as follows:
and analyzing the beat frequency signal to obtain a second-stage Brillouin frequency shift quantity, and demodulating temperature/strain information through the second-stage Brillouin frequency shift quantity.
5. A high-sensitivity sensing device based on two-stage Brillouin scattering is characterized by comprising: a narrow linewidth laser (1), the output end of the narrow linewidth laser (1) is connected with the optical splitter (3),
a first output end of the optical splitter (3) is connected with a first port of a first optical circulator (4), a second port of the first optical circulator (4) is connected with one end of a reference optical fiber (6), and a third port is connected with a first port of a second optical circulator (8); a second port of the second optical circulator (8) is connected with the other end of the reference optical fiber (6), and a third port is connected with a first input end of the optical coupler (9);
the second output end of the optical splitter (3) is connected with the first port of a third circulator (14) through a first modulator (13), the second port of the third circulator (14) is connected with one end of a sensing optical fiber (16), and the third port is connected with the first port of a fourth optical circulator (19) through the second modulator (13); a second port of the fourth optical circulator (19) is connected with the other end of the sensing optical fiber (16), and a third port is connected with a second input end of the optical coupler (9);
the output end of the pulse generator (12) is connected with the control ends of the first modulator (13) and the second modulator (17) and is used for driving the first modulator (13) and the second modulator (17) and controlling the relative delay time tau of the first modulator and the second modulator;
the output end of the coupler (9) is connected with a photoelectric detector (10), the photoelectric detector (10) is used for receiving beat frequency signals of two-stage Brillouin spontaneous scattering signals generated in the sensing optical fiber (16) and the reference optical fiber (6), and the output end of the photoelectric detector is connected with a spectrum analyzer (11); the spectrum analyzer (11) is used for collecting and analyzing beat frequency signals and demodulating temperature/strain information in the sensing optical fiber.
6. The high-sensitivity sensing device based on two-stage Brillouin scattering according to claim 5, further comprising a first erbium-doped fiber amplifier (2), wherein the first erbium-doped fiber amplifier (2) is arranged between the narrow-linewidth laser (1) and the optical splitter (3) and is used for amplifying an output signal of the narrow-linewidth laser (1).
7. The two-stage Brillouin scattering-based high-sensitivity sensing device according to claim 5, further comprising a first optical filter (5) and a second optical filter (15), wherein the first optical filter (5) is arranged between the third port of the first optical circulator (4) and the first port of the second optical circulator (8) and is used for filtering stray signals in the Brillouin backscattering reference light; and the second optical filter (15) is arranged between the third port of the second optical circulator (14) and the first port of the fourth optical circulator (19) and is used for filtering stray signals in the Brillouin backscattering sensing light.
8. The high-sensitivity sensing device based on two-stage Brillouin scattering according to claim 7, further comprising a second erbium-doped fiber amplifier (7) and a pulsed light amplifier (18);
the second erbium-doped fiber amplifier (7) is arranged between the first optical filter (5) and the first port of the second optical circulator (8), and the pulse optical amplifier (18) is arranged between the second optical filter (15) and the first port of the fourth optical circulator (19).
9. The two-stage Brillouin scattering-based high-sensitivity sensing device according to claim 5, wherein the optical splitter (3) is a 1 x 2 fiber coupler.
10. A highly sensitive sensing device based on two-stage Brillouin scattering according to claim 5, characterized in that the first modulator (13) and the second modulator (17) are electro-optical intensity modulators.
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