CN113566860B - Chaotic Raman fiber sensing device based on Brillouin and Raman third-order combined amplification - Google Patents
Chaotic Raman fiber sensing device based on Brillouin and Raman third-order combined amplification Download PDFInfo
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Abstract
The invention belongs to the field of temperature safety detection in a distributed optical fiber sensing technology, in particular to a chaotic Raman distributed optical fiber sensing device based on combined amplification of Brillouin and Raman third-order, which comprises a first chaotic laser, wherein chaotic laser emitted by the first chaotic laser is divided into two beams, one beam is modulated into pulse light and then divided into a reference beam and a signal beam, the reference beam is received by a first photoelectric detector, and the signal beam enters a sensing optical fiber after passing through a wavelength division multiplexer; the other beam carries out double-sideband modulation and filters out a low-frequency sideband, so that a high-frequency sideband enters a sensing optical fiber from the other end to carry out stimulated Brillouin amplification on pulse light, back anti-Stokes light generated by Raman scattering of the pulse light is output from the sensing optical fiber and is output to a second photoelectric detector through a wavelength division multiplexer, and chaotic laser signals output by a second chaotic laser and a third chaotic laser respectively serve as pumping light to enter the sensing optical fiber in opposite directions. The invention increases the sensing distance of the system by the third-order joint amplification, which can reach 100km.
Description
Technical Field
The invention belongs to the field of temperature safety detection in a distributed optical fiber sensing technology, and particularly relates to a chaotic Raman distributed optical fiber sensing device which can realize a sensing distance of 100km and is based on Brillouin and Raman third-order combined amplification.
Background
The distributed optical fiber Raman sensing system can realize continuous distributed temperature monitoring and has the advantages of electromagnetic interference resistance, corrosion resistance, electric insulation, high sensitivity, fire prevention, explosion prevention and the like. In the sensing optical fiber, the pulse laser propagates in the optical fiber to generate two raman scattering signals, namely stokes light and anti-stokes light, wherein the anti-stokes signal is more easily affected by temperature and is more sensitive to the temperature. Therefore, stokes light and anti-Stokes light can be used for temperature demodulation, and distributed temperature monitoring along the optical fiber is realized. The prior distributed optical fiber Raman temperature sensing technology has very wide application prospect, and is mainly applied to the fields of disaster detection, protection, alarm and the like of coal mines, tunnels, bridges, highways, high-rise buildings and the like.
The sensing distance and the measuring precision of the distributed temperature sensing system mainly depend on a temperature demodulation method, and at present, the temperature demodulation method comprises two types of single-path demodulation and double-path demodulation. The single-path demodulation method is to determine the temperature by utilizing the Raman anti-Stokes back-scattered light through the sensing optical fiber; the two-way demodulation method is to demodulate the temperature using the ratio of anti-stokes scattered light to rayleigh or stokes scattered light. The method relies on the intensity of the raman anti-stokes back scattering light, however, the intensity of the raman backward anti-stokes scattering signal is weak, so that the sensing distance of 30km can only be realized at present, and the method has higher requirements on the sensing distance in engineering applications such as tunnels, bridges and the like.
Based on the above, it is necessary to invent a novel distributed optical fiber raman sensing device and method, which can improve the intensity of raman anti-stokes back scattering light, so as to solve the technical problem that the sensing distance of the existing distributed optical fiber raman sensing system cannot break through 30 km.
Disclosure of Invention
In order to solve the technical problem that the sensing distance is difficult to break through 30km due to the fact that the sensing distance of the existing distributed optical fiber Raman sensing system is limited by Raman scattering signal intensity, the invention provides a Raman distributed optical fiber sensing device based on Brillouin and Raman third-order combined amplification, which can amplify Raman scattering signals and finally realize the ultra-long sensing distance of 100km.
In order to solve the technical problems, the invention adopts the following technical scheme: a raman distributed optical fiber sensing device based on brillouin and raman third-order joint amplification, comprising: the device comprises a first chaotic laser, a second chaotic laser and a third chaotic laser, wherein chaotic laser emitted by the first chaotic laser is divided into two beams after passing through a first coupler, one beam is modulated into pulse light by a first modulator, the pulse light is divided into a reference beam and a signal beam after passing through a first isolator and a second coupler in sequence, the reference beam is received by a first photoelectric detector, and the signal beam enters a sensing optical fiber after passing through a wavelength division multiplexer and a third coupler in sequence; the other beam is subjected to double-sideband modulation through a second modulator, a low-frequency sideband is filtered through a filter, a high-frequency sideband enters a sensing optical fiber from the other end through a fourth coupler to perform stimulated Brillouin amplification on pulse light, back anti-Stokes light generated by Raman scattering of the pulse light in the sensing optical fiber is output through a third coupler and returns to a wavelength division multiplexer, the back anti-Stokes light is output to a second photoelectric detector through the wavelength division multiplexer, chaotic laser signals output by the second chaotic laser and the third chaotic laser are used as pumping light and enter the sensing optical fiber in opposite directions through the fourth coupler and the third coupler, and the bandwidth of the anti-Stokes light is within the Raman gain bandwidth of the sensing optical fiber.
The center wavelength of the first chaotic laser is 1550nm, the center wavelengths of the second chaotic laser and the third chaotic laser) are 1350nm, and the modulation frequency of the second modulator is 10.8GHz.
The Raman distributed optical fiber sensing device based on the combined amplification of Brillouin and Raman third-order further comprises a second isolator, wherein the second isolator is arranged between the fourth coupler and the sensing optical fiber.
The Raman distributed optical fiber sensing device based on the combined amplification of Brillouin and Raman third-order further comprises a first arbitrary waveform generator and a second arbitrary waveform generator, wherein the first arbitrary waveform generator and the second arbitrary waveform generator are respectively used for driving a second modulator and a first modulator.
The Raman distributed optical fiber sensing device based on the Brillouin and Raman third-order combined amplification further comprises a data acquisition card, and signal output ends of the first photoelectric detector and the second photoelectric detector are connected with the data acquisition card.
The temperature of the Raman distributed optical fiber sensing device based on the combined amplification of Brillouin and Raman third-order is demodulated according to the calculation formula:
wherein T is 1 Representing the temperature of the measuring location, C peak Representing the positive peak value of the correlation,represents L 1 Attenuation information at the location, i represents the number of data points, P i The power of the ith data point of the chaotic pulse laser is represented, W represents pulse width, fs represents sampling rate and K represents sampling rate as Representing coefficients related to the raman anti-stokes back-scatter cross-section, lambda as Is the wavelength of the raman anti-stokes scattering signal, k is the boltzmann constant, Δν is the raman shift, h is the planck constant, T 0 Indicating the temperature of the non-temperature change region.
The Raman distributed optical fiber sensing device based on the combined amplification of Brillouin and Raman third-order has a temperature abrupt change region position L during temperature demodulation 1 The calculation formula of (2) is as follows:
L 1 ＝a 0 ·c/(2n 0 ·f s )；
wherein a is 0 Representing the number of corresponding delay sampling points when the correlation coefficient presents a positive peak value, n 0 Representing the refractive index in the sensing fiber, c representing the speed of light, f s Representing the sampling rate.
Compared with the prior art, the invention has the following beneficial effects: according to the invention, the chaotic laser with the wavelength of 1550nm is modulated by a second modulator through a sine signal to perform double-sideband modulation, so that 1549.91nm laser passing through a filter provides amplification gain for the chaotic pulse laser with the wavelength of 1550nm, which is transmitted by a sensing optical fiber, and the chaotic Raman anti-Stokes laser signal is enhanced; in addition, 1350nm laser generated by the two chaotic lasers provides forward and backward amplification gain for scattered light of 1450nm of Raman backward anti-Stokes, and finally, chaotic differential reconstruction and cross-correlation processing are carried out on a chaotic pulse reference signal and a chaotic Raman anti-Stokes scattered signal amplified by a third-order combined signal, so that detailed information of a sensing optical fiber temperature change area can be demodulated, and the sensing distance can reach 100km.
Drawings
Fig. 1 is a schematic structural diagram of a chaotic raman fiber sensing device based on brillouin and raman third-order joint amplification according to an embodiment of the present invention;
in the figure: 1-first laser, 2-first coupler, 3-first arbitrary waveform generator, 4-second modulator, 5-second chaotic laser, 6-filter, 7-fourth coupler, 8-second isolator, 9-sensing optical fiber, 10-first modulator, the system comprises an 11-second arbitrary waveform generator, a 12-first isolator, a 13-second coupler, a 14-wavelength division multiplexer, a 15-third coupler, a 16-third chaotic laser, a 17-first photoelectric detector, an 18-second photoelectric detector and a 19-acquisition card.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in 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; all other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
As shown in fig. 1, the raman distributed sensing system based on brillouin and raman third-order combined amplification of the present invention can realize a sensing distance of 100km, and specifically includes: the first chaotic laser 1, the second chaotic laser 5 and the third chaotic laser 16, wherein the chaotic laser emitted by the first chaotic laser 1 is divided into two beams by the first coupler 2, one beam is modulated into pulse light by the first modulator 10 and then is divided into a reference beam and a signal beam by the first isolator 12 and the second coupler 13 in sequence, the reference beam is received by the first photoelectric detector 17, and the signal beam enters the sensing optical fiber 9 after passing through the wavelength division multiplexer 14 and the third coupler 15 in sequence; the other beam is subjected to double-sideband modulation through a second modulator 4, a low-frequency sideband is filtered through a filter 6, a high-frequency sideband enters a sensing optical fiber 9 from the other end after passing through a fourth coupler 7 and a second isolator 8 to carry out stimulated Brillouin amplification on pulse light, reverse anti-Stokes light generated by Raman scattering of the pulse light in the sensing optical fiber 9 is output through a third coupler 15 and returned to a wavelength division multiplexer 14, and then is output to a second photoelectric detector 18 through the wavelength division multiplexer 14, and chaotic laser signals output by the second chaotic laser 5 and the third chaotic laser 16 are used as pump light and respectively enter the sensing optical fiber 9 in opposite directions through the fourth coupler 7 and the third coupler 15, wherein the bandwidth of the anti-Stokes light is within the Raman gain bandwidth of the sensing optical fiber.
Specifically, in this embodiment, the output end of the first chaotic laser 1 is connected to the a port of the first coupler 2; the output port b of the first coupler 2 is connected with the b port of the second modulator 4; the a and c ports of the second modulator 4 are respectively connected with the arbitrary waveform generator 3 and the filter 6; the second chaotic laser 5 and the filter 6 are respectively connected with an a port and a b port of the fourth coupler 7; the c port of the fourth coupler 7 is connected with an isolator 8; the second isolator 8 is connected with the other end of the sensing optical fiber 9; the c-port of the first coupler 2 is connected with the b-port of the first modulator 10; the a and c ports of the first modulator 10 are respectively connected with an arbitrary waveform generator 11 and an isolator 12; the isolator 12 is connected with the b port of the second coupler 13; the port a and the port c of the second coupler 13 are respectively connected with the port b of the first photoelectric detector 17 and the wavelength division multiplexer 14; the port a and the port c of the wavelength division multiplexer 14 are respectively connected with the port a of the second photoelectric detector 18 and the port a of the third coupler 15; the ports b and c of the third coupler 15 are respectively connected with one end of the chaotic laser 16 and one end of the sensing optical fiber 9; the first photodetector 17 and the second photodetector 18 are connected with the acquisition card 19.
Specifically, in the present embodiment, the center wavelength of the first chaotic laser 1 is 1550nm, the center wavelengths of the second chaotic laser 5 and the third chaotic laser 16 are 1350nm, and the modulation frequency of the second modulator 4 is 10.8GHz. The second modulator 4 is used for double-sideband modulation, and the filter 6 is used for filtering out the low-frequency sidebands, so that the high-frequency sidebands and the pulse light meet the stimulated Brillouin amplification condition, the pulse light can be amplified, and the strength of a sensing signal is increased.
Specifically, in the present embodiment, the first modulator 10 and the second modulator 4 are acousto-optic modulators, and the first coupler 2, the second coupler 13, the third coupler 15, and the fourth coupler 7 are each 50:50 by 2 fiber coupler.
Specifically, the sensing device in the present embodiment further includes a first arbitrary waveform generator 3 and a second arbitrary waveform generator 11, and the first arbitrary waveform generator 3 and the second arbitrary waveform generator 11 are used to drive the second modulator 4 and the first modulator 10, respectively.
The working principle of the embodiment of the invention is as follows: the chaotic continuous light with the center wavelength of 1550nm emitted by the chaotic laser 1 passes through the first coupler 2 and is split into two beams. One of the chaotic lasers is emitted from the c port of the optical fiber coupler 2, modulated into chaotic pulse light through the first modulator 10, and the pulse light reaches 1 after passing through the first isolator 12: 99, wherein the reference light is detected by the first photodetector 17 and used as a reference path, the other signal light reaches the sensing optical fiber 9 through the wavelength division multiplexer 14 and the third coupler 15 and is subjected to raman scattering, the generated chaotic raman backward anti-stokes scattering signal is output from the port b, the other continuous light is modulated by the first modulator 4 modulated by the sinusoidal signal, so that the 1550nm incident chaotic signal generates brillouin frequency shift, the peak of the original 1550nm disappears to form the doublet of 1549.91nm and 1550.09nm, the 1549.91nm continuous chaotic light is obtained after passing through the filter 6, enters from the other end of the sensing optical fiber through the first coupler 7 and the isolator 8 and meets the 1550nm chaotic signal light in the sensing optical fiber to provide gain for the chaotic light, and the 1550nm incident chaotic signal light in the sensing optical fiber is stimulated to have stimulated brillouin enhancement in intensity. In addition, the second chaotic laser 5 emits pump light with the center wavelength of 1350nm, and the pump light enters the sensing optical fiber 9 from the other end after passing through the fourth coupler 7 and the isolator 8, so that the raman backward anti-stokes scattering signal is forward modulated, and the signal is enhanced; the 1350nm pump light emitted by the third chaotic laser source 16 also enters the sensing optical fiber 9 after passing through the optical fiber coupler 15, and the back scattering signal is subjected to back modulation, so that the signal is enhanced again, and the signal enhancement principle is as follows: when the emission wavelength of the pump light is 70-100 nm lower than the wavelength of the signal light, and the weak light signal (anti-Stokes scattered light) and the injected strong pump light are transmitted in the optical fiber at the same time, when the bandwidth of the weak light signal is within the Raman gain bandwidth of the sensing optical fiber, the pump light energy can be transferred into the weak light signal through the stimulated Raman scattering effect, so that the weak light signal is amplified.
The wavelength division multiplexer 14 emits raman backward anti-stokes scattered light having a wavelength of 1450nm, which is detected by the second photodetector 18. Finally, signals detected by the first photoelectric detector 17 and the second photoelectric detector 18 are collected by a data collection card 19, and the obtained chaotic pulse reference signal and the chaotic Raman anti-Stokes scattering signal amplified by the third-order combined signal are demodulated to obtain temperature information along the optical fiber.
The demodulation principle of the sensing device of the invention is as follows: carrying out differential reconstruction on the acquired chaotic Raman back-scattered light signals to obtain reconstructed Raman scattered signals; performing cross-correlation operation on the chaotic pulse reference signal and the reconstructed chaotic Raman anti-Stokes signal to obtain a correlation peak C of the chaotic pulse reference signal and the reconstructed chaotic Raman anti-Stokes signal peak According to the position of the correlation peak value, the position and the temperature T of the temperature abrupt change region along the optical fiber can be calculated 1 。
The demodulation and positioning principle for temperature measurement in the embodiment of the present invention is described in detail below.
1. Chaotic Raman anti-Stokes signal and chaotic pulse reference signal acquisition
(1) And (3) acquisition of chaotic Raman anti-Stokes signals.
In temperature demodulation, let the laser pulse width be W, the backward Raman anti-Stokes scattering signal (anti-Stokes) intensity at the position of the sensing fiber L is:
wherein P is the incident power of the pulse laser, K as Representing the coefficient related to the raman anti-stokes backscattering cross section, S being the backscattering factor of the fiber, λ as Is the wavelength of the raman anti-stokes scattering signal, phi e Representing the pulse laser light flux, alpha, coupled into the fiber 0 、α as The loss coefficients of incident light and anti-Stokes light in the sensing optical fiber per unit length are respectively L is the length of the sensing light, R as (T) is the temperature modulation function of the anti-stokes scattered light:
Δν is raman shift, h is planck constant, k is boltzmann constant, and T is sensing fiber temperature.
In fact, in the distributed optical fiber raman sensing system, the detection signal is a pulse signal, so that the information collected by the high-speed data collection card at a certain moment is not the light intensity information of one point at the position of the optical fiber L, but the superposition of the light intensity information of a section of optical fiber with the sensing distance equal to half pulse width of the whole pulse signal. The detection signal used in the Raman distributed optical fiber sensing method based on the combined amplification of Brillouin and Raman third-order is a chaotic pulse signal, and the power of the whole pulse signal is in a random fluctuation state. Therefore, when the chaotic pulse sequence with the pulse width W of the detection signal is adopted, the chaotic Raman anti-Stokes signal intensity at the position of the sensing optical fiber L is acquired by the high-speed data acquisition card and can be expressed as follows:
wherein P is i Power of ith data point of chaotic pulse laser, f s For sampling rate W.f s Is the chaotic pulse signal at f s The number of unit pulse data points at the sampling rate, W is the pulse width, W i For pulse width, W, corresponding to i data points i ＝i/f s ，Back-scattering factor of anti-stokes photons modulated by temperature per unit length, c is the propagation speed of light in the sensing fiber, n 0 Is the refractive index of the sensing fiber.
(2) Acquisition of chaotic pulse reference signals
The continuous light emitted by the chaotic laser 1 is modulated into pulse light after passing through a first modulator 10 driven by a second arbitrary waveform generator 11, the pulse laser passes through an a port of a second coupler 13, and a reference signal is collected by an acquisition card 19, wherein the reference signal is as follows:
I ref (i)＝P i wherein i is more than or equal to 1 and is more than or equal to W.f s ； (4)
2. Chaotic Raman anti-Stokes signal and chaotic pulse reference signal processing
(1) The differential reconstruction method is used for processing the chaotic Raman anti-Stokes signals.
And collecting the obtained chaotic Raman anti-Stokes scattered light signals, wherein each sampling point is the superposition of light intensity information of the whole chaotic pulse sequence in the length of an optical fiber with half pulse width. Based on the method, the backscattering signal is reconstructed, and the expression of the time domain differential reconstruction method is as follows:
wherein F is as (L, i) reconstructing the chaotic raman back-scattered signal.
Let the temperature of the temperature change area be T 1 The temperature change area is L 1 The temperature of the non-temperature-change region is T 0 After differential reconstruction treatment, a non-temperature mutation region reconstructed chaotic Raman back scattering signal of 0 and a temperature burst are obtainedReconstruction of the position of the change point raman back-scattered signal F as (L 1 ,P i ) Expressed as:
wherein,represents L 1 Attenuation information at location,/->(2) And positioning by using a cross-correlation compression method.
And carrying out cross-correlation operation on the chaotic pulse reference signal and the reconstructed chaotic Raman back scattering signal, wherein the operation formula is as follows:
wherein C (a) is a cross-correlation operation formula, N represents the total sampling point number of the reconstructed chaotic Raman back scattering signal, and F as (n) represents the nth sampling point of the reconstructed chaotic Raman back-scattered signal, I ref (n+a) represents a chaotic pulse reference signal delayed by a sampling points.
When the reference signal is delayed by a 0 The phase relation number from the sampling point to the initial end point position of the temperature mutation area shows a positive peak value, so that the position of the temperature mutation area can be determined as follows:
L 1 ＝a 0 ·c/(2n 0 ·f s )； (8)
(3) Positive peak demodulation temperature using cross correlation
Cross-correlating the reference signal with a reconstructed chaotic Raman back-scattered signal at a temperature mutation position, wherein a correlation positive peak value expression is as follows:
by combining the formulas (4) and (6) and expanding the formula (9) and ignoring the additional loss information, the following can be obtained:
binding R as (T)＝[exp(hΔν/kT)-1] -1 Extracting temperature information of a temperature mutation area, wherein a demodulation equation is shown in a formula (11): .
Wherein T is 1 Representing the temperature of the measurement location (temperature change zone), C peak Represents the correlation positive peak value, i represents the number of data points, and P i The power of the ith data point of the chaotic pulse laser is represented, W represents pulse width, fs represents sampling rate and K represents sampling rate as Representing coefficients related to the raman anti-stokes back-scatter cross-section, lambda as Is the wavelength of the raman anti-stokes scattering signal, k is the boltzmann constant, Δν is the raman shift, h is the planck constant, T 0 Indicating the temperature of the non-temperature change region.
The invention provides a Raman distributed optical fiber sensing device based on Brillouin and Raman third-order combined amplification, which performs amplification for three times, wherein the first time is to perform optical amplification on incident pulse light by using stimulated Brillouin scattering, the second and third times are to perform forward amplification and reverse amplification on a Raman back scattering signal by using stimulated Raman scattering, so that the signal intensity of anti-Stokes light is greatly increased, the sensing distance of a system is improved, and the temperature positioning and demodulation are performed by using a time domain differential reconstruction method, so that the precision of the system is improved.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.
Claims (6)
1. A raman distributed optical fiber sensing device based on brillouin and raman third-order combined amplification, comprising: the device comprises a first chaotic laser (1), a second chaotic laser (5) and a third chaotic laser (16), wherein chaotic laser emitted by the first chaotic laser (1) is divided into two beams after passing through a first coupler (2), one beam is modulated into pulse light by a first modulator (10), the pulse light is divided into a reference beam and a signal beam after passing through a first isolator (12) and a second coupler (13) in sequence, the reference beam is received by a first photoelectric detector (17), and the signal beam enters a sensing optical fiber (9) after passing through a wavelength division multiplexer (14) and a third coupler (15) in sequence; the other beam is subjected to double-sideband modulation through a second modulator (4), a low-frequency sideband is filtered through a filter (6), a high-frequency sideband enters a sensing optical fiber (9) from the other end through a fourth coupler (7) to carry out stimulated Brillouin amplification, reverse anti-Stokes light generated by Raman scattering of the pulse light in the sensing optical fiber (9) is output through a third coupler (15) and returned to a wavelength division multiplexer (14), and then is output to a second photoelectric detector (18) through the wavelength division multiplexer (14), chaotic laser signals output by a second chaotic laser (5) and a third chaotic laser (16) are used as pump light to enter the sensing optical fiber (9) in a facing mode through the fourth coupler (7) and the third coupler (15), and the bandwidth of the anti-Stokes light is within the Raman gain bandwidth of the sensing optical fiber;
when the temperature is demodulated, the calculation formula of the temperature is as follows:
wherein T is 1 Representing the temperature of the measuring location, C peak Representing the positive peak value of the correlation,indicating the temperature abrupt change position L 1 Attenuation information at, K as Representing coefficients related to the raman anti-stokes back-scatter cross-section, lambda as Is the wavelength of the raman anti-stokes scattering signal, k is the boltzmann constant, Δν is the raman shift, h is the planck constant, T 0 Representing the temperature of the non-temperature change region;
correlation positive peak C peak The method is obtained by taking a positive peak value after carrying out cross-correlation operation on a chaotic pulse reference signal and a reconstructed chaotic Raman backward scattering signal, and the calculation formula of the cross-correlation operation is as follows:
wherein C (a) is a cross-correlation coefficient, I ref (n+a) represents a chaotic pulse reference signal delayed by a sampling points, F as (n) represents a reconstructed chaotic raman back-scattered signal of an nth sampling point;
the expression for reconstructing the time domain differential signal of the chaotic Raman back scattering signal is as follows:
wherein F is as (L, I) represents a reconstructed chaotic Raman back-scattered signal obtained by a time domain differential signal reconstruction operation, I as (L) andrespectively indicate the position of the sensing optical fiber L and +.>The intensity of the backward raman anti-stokes light at the location, i represents the data point, f s Represents the sampling rate, c represents the speed of light, n 0 Indicating the refractive index in the fiber.
2. The raman distributed optical fiber sensing device based on the combined amplification of brillouin and raman third order according to claim 1, wherein the center wavelength of the first chaotic laser (1) is 1550nm, the center wavelengths of the second chaotic laser (5) and the third chaotic laser (16) are 1350nm, and the modulation frequency of the second modulator (4) is 10.8GHz.
3. A raman distributed optical fiber sensing device based on combined brillouin and raman third order amplification according to claim 1, characterized by further comprising a second isolator (8), said second isolator (8) being arranged between the fourth coupler (7) and the sensing optical fiber (9).
4. A raman distributed optical fiber sensing device based on combined brillouin and raman third order amplification according to claim 1, further comprising a first arbitrary waveform generator (3) and a second arbitrary waveform generator (11), said first arbitrary waveform generator (3) and second arbitrary waveform generator (11) being used for driving the second modulator (4) and the first modulator (10), respectively.
5. A raman distributed optical fiber sensing device based on combined brillouin and raman third-order amplification according to claim 1, further comprising a data acquisition card (19), wherein the signal output ends of the first photodetector (17) and the second photodetector (18) are connected to the data acquisition card (19).
6. The raman distributed optical fiber sensing device based on the combined amplification of brillouin and raman third order according to claim 1, wherein the temperature abrupt change area position L is at the time of temperature demodulation 1 The calculation formula of (2) is as follows:
L 1 ＝a 0 ·c/(2n 0 ·f s )；
wherein a is 0 Representing the number of corresponding delay sampling points when the correlation coefficient presents a positive peak value, n 0 Indicating sensing optical fiberThe refractive index of (c) represents the speed of light, f s Representing the sampling rate.
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