Monitoring equipment capable of simultaneously measuring distributed temperature and distributed sound waves

Abstract

The utility model discloses a monitoring device capable of simultaneously measuring distributed temperature and distributed sound waves. Comprising a light source, a first optical fiber coupler, a pulse modulator, an optical amplifier, an optical fiber circulator, a wavelength division multiplexer, a few-mode optical fiber multiplexer, a few-mode optical fiber, a second optical fiber coupler, a double-balance detector, a first photoelectric detector, a second photoelectric detector, a third photoelectric detector and an information acquisition and processing unit. The Raman signal and the Rayleigh signal of the few-mode optical fiber are used for detection, the optical fiber attenuation test can be carried out by using the intensity distribution of one path of Rayleigh scattering light to compensate the Raman scattering signal, and the Raman scattering signal is compensated by using the characteristics of high injection threshold power, controllable inter-mode interference and the like of the few-mode optical fiber. The problems that single-mode optical fiber temperature measurement precision is low, a temperature curve drifts along with optical fiber attenuation, and multi-mode optical fiber vibration related Rayleigh scattering signals are insufficient in stability are effectively solved.

Description

Technical Field

[0001] The utility model belongs to the field, and more specifically, relates to a monitoring device capable of simultaneously measuring distributed temperature and distributed sound waves. Background Art

[0002] Compared with traditional sensors, fiber optic sensors have the advantages of small size, wide bandwidth, high sensitivity, no electromagnetic interference, corrosion resistance, high temperature resistance, high pressure resistance, and adaptability to harsh environments. Since the last century, more than a hundred types of fiber optic sensors have been developed. It has been proven that fiber optic sensors can detect more than 70 physical quantities such as strain, displacement, pressure, speed, acceleration, torque, angular velocity, temperature, current, voltage, concentration, flow, flow rate, as well as magnetism, sound, light, and radiation. Its application has penetrated into the fields of energy, mining, national defense and military, medicine and biology, and intelligent structures.

[0003] A distributed optical fiber sensing system can be defined as a system that can measure the variation of the measured parameter along the entire continuous length of the optical fiber in the form of a continuous function of distance. Distributed temperature and acoustic wave sensing systems usually arrange optical fibers along the temperature field and vibration field, measure the scattered light carrying temperature and vibration information when the light is transmitted in the optical fiber, and use OTDR (Optical Time Domain Reflectometer) technology to measure and monitor the spatial distribution of temperature and vibration along the optical fiber transmission path and the information that varies with time.

[0004] When light enters the optical fiber, the interaction between the photons and the optical fiber medium causes the light to change direction, which is light scattering. When the photons interact with the silica molecules in the optical fiber, two situations occur: energy exchange and no energy exchange.

[0005] When photons collide elastically with the fiber ring without exchanging energy, this process is called Rayleigh scattering. The optical time domain reflectometer based on Rayleigh scattering is the earliest and most mature technology so far. Phase-sensitive optical time domain reflectometer (Φ-OTDR) is based on Rayleigh scattering technology and extracts the phase information of Rayleigh scattered light in the optical fiber link to demodulate the vibration information.

[0006] When photons collide inelastically with the optical fiber medium and exchange energy, this process produces the Raman scattering effect. The distributed optical fiber temperature sensor based on Raman scattering is the first commercial product abroad, and it also has the most practical technology. Most of them are based on the distributed optical fiber temperature sensor based on optical time-domain Raman scattering reflectometer (ROTDR), which sends a short laser pulse to the optical fiber and then measures the backscattered Raman light. The optical signal contains the loss and temperature distribution information along the optical fiber.

[0007] At present, the temperature-vibration dual-parameter detection system based on the fiber Bragg grating principle is limited to point-type and cannot achieve long-distance distributed detection; the Raman-Rayleigh OTDR integrated system based on single-mode optical fiber is time-division multiplexing and cannot achieve dual-parameter detection of temperature and sound waves at the same time. Moreover, the spontaneous Raman scattered light is very weak, so the fiber input power needs to be increased. Single-mode optical fibers share the same light source, and there is a mismatch in the optical power of the two systems, which causes modulation instability. Utility Model Content

[0008] In response to the above defects or improvement needs of the prior art, the utility model provides a monitoring device that can simultaneously measure distributed temperature and distributed acoustic waves. It utilizes the Raman signal and Rayleigh signal of the few-mode optical fiber for detection, thereby realizing simultaneous monitoring of distributed temperature and acoustic waves based on the few-mode optical fiber.

[0009] To achieve the above-mentioned purpose, according to the utility model, a monitoring device capable of simultaneously measuring distributed temperature and distributed acoustic waves is provided, comprising a light source, a first optical fiber coupler, a pulse modulator, an optical amplifier, an optical fiber circulator, a wavelength division multiplexer, a few-mode optical fiber multiplexer, a few-mode optical fiber for reference, a few-mode optical fiber for sensing, a second optical fiber coupler, a double-balanced detector, a first photodetector, a second photodetector, a third photodetector and an information acquisition and processing unit, wherein:

[0010] The output port of the light source is connected to the input port of the first optical fiber coupler, the first output port of the first optical fiber coupler is connected to the first input port of the dual-balanced detector, the second output port of the first optical fiber coupler is connected to the first input port of the pulse modulator, the second input port of the pulse modulator is connected to the information acquisition and processing unit, the output port of the pulse modulator is connected to the input port of the optical amplifier, the output port of the optical amplifier is connected to the first port of the optical fiber circulator, the second port of the optical fiber circulator is connected to the first port of the wavelength division multiplexer, the third port of the optical fiber circulator is connected to the first port of the second optical fiber coupler, the second port of the second optical fiber coupler is connected to the second input port of the dual-balanced detector, the third output port of the second optical fiber coupler is connected to the first photodetector, the second port and the third port of the wavelength division multiplexer are connected to the second photodetector and the second photodetector respectively, the fourth port of the wavelength division multiplexer is connected to the first port of the few-mode optical fiber multiplexer, the second port of the few-mode optical fiber multiplexer is connected to the few-mode optical fiber, and the information acquisition and processing unit is respectively connected to the dual-balanced detector, the first photodetector, the second photodetector and the third photodetector.

[0011] Preferably, the light source is a single-frequency narrow-linewidth laser source.

[0012] Preferably, the light source is a 1550nm narrow line width light source.

[0013] Preferably, the pulse modulator is an acousto-optic modulator or an electro-optic modulator.

[0014] Preferably, the pulse modulator and the optical amplifier are respectively replaced by SOA devices.

[0015] Preferably, the core diameter of the few-mode optical fiber is 16 μm to 33 μm.

[0016] Preferably, the few-mode optical fiber is a two-mode, four-mode or six-mode optical fiber.

[0017] Preferably, there are two few-mode optical fibers, namely a reference few-mode optical fiber and a sensing few-mode optical fiber. The second port of the optical fiber multiplexer is connected to the reference few-mode optical fiber, and the reference few-mode optical fiber is connected to the sensing few-mode optical fiber.

[0018] Preferably, the wavelength division multiplexer is used to separate the Raman signal and the Rayleigh signal in the reflected light signal of the few-mode optical fiber, the balanced detector is used to receive the Rayleigh scattering signal of the Rayleigh signal, the first photodetector receives the Rayleigh intensity signal for receiving the Rayleigh signal, and the second photodetector and the third photodetector are respectively used to receive the Stokes light and the anti-Stokes light of the Raman signal.

[0019] Preferably, the temperature is responded to using a Raman signal, and the sound wave is responded to using a Rayleigh signal.

[0020] In general, the above technical solution conceived by the utility model can achieve the following beneficial effects compared with the prior art:

[0021] 1) The monitoring device of the utility model can simultaneously measure distributed temperature and distributed sound waves, and uses the Raman signal and Rayleigh signal of the few-mode optical fiber for detection. The Raman signal is only sensitive to temperature, and the Rayleigh signal is only sensitive to vibration (sound wave). Using this characteristic, the utility model can realize the distributed temperature-sound wave simultaneous monitoring based on the few-mode optical fiber, solve the problem that the fiber grating temperature-vibration sensing system cannot be distributed for monitoring, and solve the problem that the conventional distributed temperature and sound wave monitoring device requires two optical fibers and two systems for detection respectively. At the same time, the Raman scattering signal can be compensated by testing the attenuation of the optical fiber using the intensity distribution of one Rayleigh scattered light. The utility model uses the characteristics of the few-mode optical fiber with high injection threshold power and controllable inter-mode interference to effectively solve the problems of low temperature measurement accuracy of single-mode optical fiber, drift of temperature curve with optical fiber attenuation, and insufficient stability of vibration-related Rayleigh scattering signals of multi-mode optical fiber.

[0022] 2) The utility model is a monitoring device that can simultaneously measure distributed temperature and distributed sound waves. Combined with wavelength division multiplexing technology, it can inject a higher stimulated nonlinear threshold power than single-mode optical fiber. Under the same measurement distance conditions, it can improve the signal-to-noise ratio of the reflected light signal and improve the high spatial resolution and detection accuracy of the system. It obtains the distributed attenuation information of the optical fiber to compensate for the Raman temperature solution and ensure the temperature measurement accuracy when the optical fiber loss changes. At the same time, it uses wavelength division multiplexing technology and adopts few-mode optical fiber to detect temperature and sound waves at the same time, which can effectively reduce the system cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a structural diagram of a few-mode optical fiber sensing system in an embodiment of the utility model;

[0024] Figure 2 Schematic diagram of the demodulation algorithm used in the embodiment of the present utility model. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the utility model more clear, the utility model is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the utility model and are not used to limit the utility model. In addition, the technical features involved in each embodiment of the utility model described below can be combined with each other as long as they do not conflict with each other.

[0026] Reference Figure 1 , Figure 2 , a monitoring device capable of simultaneously measuring distributed temperature and distributed acoustic waves, comprising a light source 1, a first optical fiber coupler 2, a pulse modulator 3, an optical amplifier 4, an optical fiber circulator 5, a wavelength division multiplexer 6, a few-mode optical fiber multiplexer 7, a few-mode optical fiber for reference 8, a few-mode optical fiber for sensing 9, a second optical fiber coupler 10, a double-balanced detector 11, a first photodetector 12, a second photodetector 13, a third photodetector 14 and an information acquisition and processing unit 15, wherein:

[0027] The light source 1 preferably adopts a single-frequency narrow-linewidth laser source, and further preferably adopts a 1550nm narrow-linewidth light source. The pulse modulator 3 preferably adopts an acousto-optic modulator or an electro-optic modulator. The pulse modulator 3 and the optical amplifier 4 can be replaced by SOA devices respectively.

[0028] The output port of the light source 1 is connected to the input port 2_1 of the first optical fiber coupler 2, the first output port 2_2 of the first optical fiber coupler 2 is connected to the first input port of the double-balanced detector 11, the second output port 2_3 of the first optical fiber coupler 2 is connected to the first input port of the pulse modulator 3, the second input port of the pulse modulator 3 is connected to the information acquisition and processing unit 15, the output port of the pulse modulator 3 is connected to the input port of the optical amplifier 4, the output port of the optical amplifier 4 is connected to the first port 5_1 of the optical fiber circulator 5, the second port 5_2 of the optical fiber circulator 5 is connected to the first port 6_1 of the wavelength division multiplexer 6, and the third port 5_3 of the optical fiber circulator 5 is connected to the second optical fiber coupler 2. The first port 10_1 of the optical fiber coupler 10 is connected to the second input port of the dual balanced detector 11, the second port 10_2 of the second optical fiber coupler 10 is connected to the first photodetector 12, the second port 6_2 and the third port 6_3 of the wavelength division multiplexer 6 are connected to the second photodetector 13 and the second photodetector 13 respectively, the fourth port 6_4 of the wavelength division multiplexer 6 is connected to the first port of the few-mode fiber multiplexer 7, the second port of the few-mode fiber multiplexer 7 is connected to the few-mode fiber, and the information acquisition and processing unit 15 is connected to the dual balanced detector 11, the first photodetector 12, the second photodetector 13 and the third photodetector 14 respectively.

[0029] Furthermore, the core diameter of the few-mode optical fiber is 16 μm to 33 μm, and it can be a two-mode, four-mode or six-mode optical fiber.

[0030] Furthermore, there are two few-mode optical fibers, namely, a reference few-mode optical fiber 8 and a sensing few-mode optical fiber 9. The second port of the optical fiber multiplexer is connected to the reference few-mode optical fiber 8, and the reference few-mode optical fiber 8 is connected to the sensing few-mode optical fiber 9. The reference few-mode optical fiber 8 can be placed in a set temperature environment and the temperature is kept constant through a temperature control algorithm, and the sensing few-mode optical fiber 9 is used to sense the external ambient temperature. The Raman signals reflected by the reference few-mode optical fiber 8 and the sensing few-mode optical fiber 9 are collected in real time. Through the corresponding relationship between the Raman signal of the reference few-mode optical fiber 8 and the known ambient temperature and the real-time Raman signal of the sensing few-mode optical fiber 9, the ambient temperature of each section of the sensing few-mode optical fiber 9 can be accurately calculated.

[0031] Furthermore, the wavelength division multiplexer 6 is used to separate the Raman signal and the Rayleigh signal in the reflected light signal of the few-mode optical fiber, the balanced detector is used to receive the Rayleigh scattering signal of the Rayleigh signal, the first photodetector 12 receives the Rayleigh intensity signal for receiving the Rayleigh signal, and the second photodetector 13 and the third photodetector 14 are used to receive the Stokes light and the anti-Stokes light of the Raman signal respectively. The Raman signal is only sensitive to temperature, and the Rayleigh signal is only sensitive to vibration (sound wave). The temperature responds to the Raman signal, and the sound wave responds to the Rayleigh signal.

[0032] Conventional detection methods use single-mode to measure acoustic vibration (1550 band) and multi-mode to measure temperature (Raman band). The utility model is based on few-mode (mode between single-mode and multi-mode) and Raman and Rayleigh time-domain reflection sensing technology, and measures acoustic and temperature parameters at the same time. The power of reflected waves in different bands is detected separately, and the power of 1550 band and Raman band along with reflection position (distance) is obtained, which improves the power and makes measurement easier.

[0033] The narrow linewidth light source 1 passes through the first fiber coupler 2, the pulse modulator 3 and the optical amplifier 4. The amplified laser passes through the fiber circulator 5 and the wavelength division multiplexer 6. The 1550nm port of the wavelength division multiplexer 6 is injected into the few-mode fiber through the single-mode few-mode fiber multiplexer 7.

[0034] The reflected light signal is divided into two paths: one path contains Raman-Stokes light and anti-Stokes light, which enters the second photodetector 13 and the third photodetector 14 through the wavelength division multiplexer 6 and is converted into an electrical signal for temperature signal resolution; the other path contains Rayleigh scattered light, which passes through the fiber circulator 5 and the second fiber coupler 10. One port of the second fiber coupler 10 is connected to the first photodetector 12, which is used for detecting the fiber distributed attenuation. At the same time, the measurement of the fiber distributed attenuation is used to compensate for the temperature resolution of the Raman system. The other port of the second fiber coupler 10 is connected to the optical port of the dual balanced detector 11, which is coherent with the optical signal of the first fiber coupler 2 connected to the dual balanced detector 11, and is used for the resolution of the acoustic wave signal. The Rayleigh scattered signal is received by the balanced detector, the Rayleigh intensity signal is received by the first photodetector 12, and the Raman signal is divided into Stokes light and anti-Stokes light, which are received by the second photodetector 13 and the third photodetector 14 respectively.

[0035] The information acquisition and processing unit 15 sends a pulse modulation signal to the pulse modulator 3, generates a pulse laser to be injected into the sensing few-mode optical fiber, and generates a synchronous acquisition trigger signal at the same time, triggering the acquisition module of the information acquisition and processing unit 15 to simultaneously acquire the Raman and Rayleigh scattering signals distributed along the optical fiber carrying temperature, sound wave, and attenuation information. The signal processing module of the information acquisition and processing unit 15 calculates the temperature and sound wave signals according to the demodulation algorithm.

[0036] The utility model preferably adopts a two-mode optical fiber to build a system, ensures the injection and reception of more laser energy through a few-mode optical fiber coupling device, and separates the reflected Raman and Rayleigh signals by a wavelength division multiplexing device. Since Raman scattered light is only sensitive to temperature, and Rayleigh scattered light is only sensitive to vibration signals, it can achieve simultaneous distinguishable detection of temperature and vibration.

[0037] Conventional temperature-vibration dual-parameter detection systems based on the fiber Bragg grating principle are limited to point-type and cannot achieve long-distance distributed detection; the Raman-Rayleigh OTDR integrated system based on single-mode fiber belongs to time division multiplexing and cannot achieve dual-parameter simultaneous detection. Moreover, the spontaneous Raman scattered light is very weak, so it is necessary to increase the fiber input power. In single-mode fiber, the same light source is shared, and there is a mismatch in the optical power of the two systems, which causes modulation instability. The utility model proposes and experimentally verifies a temperature and acoustic wave simultaneous monitoring device based on few-mode fiber, combined with a time-division wavelength division multiplexing system, using one light source and one optical fiber, which can realize the simultaneous distinguishable detection of distributed temperature and acoustic wave dual parameters, while improving the measurement accuracy and reducing the system cost. The technical solution proposed by the utility model has great application prospects in actual industrial applications.

[0038] The distributed temperature and acoustic wave simultaneous monitoring equipment based on few-mode optical fiber can use two-mode, four-mode or six-mode few-mode optical fiber, which shares a 1550nm narrow linewidth light source. The wavelength division multiplexer 6 is used to separate the Raman scattered light and the Rayleigh scattered light, and the Raman signal and the Rayleigh signal are respectively resolved to realize the monitoring of the temperature and acoustic wave signals distributed along the optical fiber.

[0039] Raman scattering temperature measurement of few-mode optical fiber, assuming that the optical power of Stokes light and the optical power of anti-Stokes light are P s and P as , when the initial temperature is T0 and at the length z0 of the optical fiber, the ratio of the optical power of the Stokes light to the optical power of the anti-Stokes light can be expressed as:

[0040]

[0041] Where h is Planck's constant; k is Boltzmann's constant; Ks and Ka are the correlation coefficients of the Raman scattering cross sections of Stokes light and anti-Stokes light in the optical fiber; Vs and Va are the frequencies of the Raman photons of Stokes light and anti-Stokes light, respectively; α a , α s is the transmission loss coefficient of the optical fiber for anti-Stokes light and Stokes light related to the optical fiber length, Δv is the Raman frequency shift of the optical fiber, and the unit of T0 is the absolute temperature in Kelvin.

[0042] When the temperature is T, at the fiber length z, the ratio of the optical power of Stokes light to the optical power of anti-Stokes light can be expressed as:

[0043]

[0044] In practical applications, the stability of distributed fiber temperature sensing system (DTS) components may vary with the environment. Therefore, a known reference temperature T is introduced at the length z0 of the fiber, using the ratio of the temperature and the corresponding light intensity of the few-mode fiber. z0 By comparing the temperature at the length z0 of the optical fiber, the real-time temperature T at z along the optical fiber z The calculation is as follows:

[0045]

[0046] If the attenuation along the optical fiber changes suddenly during long-term operation, the attenuation distribution along the optical fiber can be obtained based on the real-time measured Rayleigh signal curve, and the temperature solution can be compensated to ensure the accuracy of temperature measurement.

[0047] The Rayleigh scattered acoustic wave detection of few-mode optical fiber adopts heterodyne coherent detection technology. Heterodyne coherent detection is achieved by optically beating local light with backward Rayleigh scattered light. It can not only effectively filter out the influence of frequency-independent noise, but also play the role of phase-locked amplification; at the same time, the intensity of the demodulated signal is no longer proportional to the scattered light intensity, but proportional to the scattered light electric field amplitude, so that the signal-to-noise ratio deteriorates more slowly with the position of the optical fiber, which is conducive to the expansion of the sensing length.

[0048] The corresponding heterodyne coherent detection structure uses an orthogonal (IQ) phase demodulation algorithm for phase demodulation. The narrow linewidth laser light source 1 emits a continuous light with an angular frequency of 0, which is divided into two parts by a coupler. The part with a smaller splitting ratio is used as the local oscillator light, and the other part is modulated into a detection pulse after passing through a modulator. If it is modulated by an AOM, the modulated pulse light will produce a certain frequency shift, and the frequency shift amount is determined by the AOM itself. The detection pulse is amplified by EDFA and enters the sensing fiber. The backward Rayleigh scattered signal generated by the sensing fiber passes through a circulator and enters a balanced detector to beat with the local oscillator light and complete the photoelectric conversion. The beat signal is collected by the data acquisition card and uploaded to the host computer for data processing. When an external vibration signal acts on the optical fiber, the beat signal will change accordingly. The vibration signal can be demodulated by demodulating the phase change of the beat signal.

[0049] Assume that the angular frequency of the light emitted by the narrow linewidth laser is ω 0 , the frequency shift of AOM is Δω, then the interference signal E R (t) and the local oscillator optical signal E LO (t) can be expressed as:

[0050] E R (t) = A R exp[j(ω 0 +Δω)t+φ 1 (t)]

[0051] ELO (t) = A LO exp[jω 0 t+φ 2 (t)] (4)

[0052] Among them, A R and A LO are the intensities of the interference signal and the local oscillator light, respectively, 1 (t) and φ 2 (t) are the initial phases of the interference signal and the local oscillator light signal, j is an imaginary unit, and t is the real time.

[0053] The two are beat by the balanced detector and then the output signal I 0 (t) is:

[0054] I 0 (t) = 2A R A LO cos[(ω 0 +Δω)t+φ 1 (t)]cos[(ω 0 t+φ 2 (t)]

[0055] =A R A LO {cos[(2ω 0 +Δω)t+φ 1 (t)+φ 2 (t)]+cos[Δωt+φ 1 (t)-φ 2 (t)]} (5)

[0056] The first term in the formula contains the double frequency signal of light, which cannot be detected by the photodetector. Therefore, the output signal of the photodetector can be expressed as: I 0 (t) = Acos[Δωt+φ(t)].

[0057] The output signal is modulated and demodulated orthogonally. The algorithm principle diagram is as follows: Figure 2 As shown. The beat frequency signal I of the interference signal and the local oscillator light signal 0 (t), all the way means I 0 (t)×cos(Δωt), one way represents I 0 (t)×sin(Δωt))( Figure 2There are two multiplication signs "×" in the circle, which represent multiplication). The interference signal is multiplied by cos(Δωt) and sin(Δωt) which are orthogonal to each other, and then filtered. The interference signal is multiplied by cos(Δωt), and the local oscillator signal is multiplied by sin(Δωt), and then filtered. After filtering, the upper path represents the cosine signal of the vibration signal phase, and the lower path represents the sine signal of the vibration signal phase. The two paths are divided ( Figure 2 The symbol of a slash in the circle, “ / ” represents the division of two signals), and the tangent signal of the vibration signal phase is obtained. Finally, the phase information of the vibration signal obtained by the arc tangent calculation is expressed as:

[0058]

[0059]

[0060] Among them, A is A R and A LO The product of φ(t) = φ 0 (t)+Δφ,φ 0 (t) is the initial phase difference between the interference signal and the local oscillator light, and Δφ is the phase change caused by the disturbance signal.

[0061] Then the vibration phase signal φ(t) is expressed as:

[0062]

[0063] It is easy for those skilled in the art to understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A monitoring device capable of simultaneously measuring distributed temperature and distributed sound waves, characterized in that: The device comprises a light source, a first optical fiber coupler, a pulse modulator, an optical amplifier, an optical fiber circulator, a wavelength division multiplexer, a few-mode optical fiber multiplexer, a few-mode optical fiber for reference, a few-mode optical fiber for sensing, a second optical fiber coupler, a double-balanced detector, a first photodetector, a second photodetector, a third photodetector and an information acquisition and processing unit, wherein: The output port of the light source is connected to the input port of the first optical fiber coupler, the first output port of the first optical fiber coupler is connected to the first input port of the dual-balanced detector, the second output port of the first optical fiber coupler is connected to the first input port of the pulse modulator, the second input port of the pulse modulator is connected to the information acquisition and processing unit, the output port of the pulse modulator is connected to the input port of the optical amplifier, the output port of the optical amplifier is connected to the first port of the optical fiber circulator, the second port of the optical fiber circulator is connected to the first port of the wavelength division multiplexer, the third port of the optical fiber circulator is connected to the first port of the second optical fiber coupler, the second port of the second optical fiber coupler is connected to the second input port of the dual-balanced detector, the third output port of the second optical fiber coupler is connected to the first photodetector, the second port and the third port of the wavelength division multiplexer are connected to the second photodetector and the second photodetector respectively, the fourth port of the wavelength division multiplexer is connected to the first port of the few-mode optical fiber multiplexer, the second port of the few-mode optical fiber multiplexer is connected to the few-mode optical fiber, and the information acquisition and processing unit is respectively connected to the dual-balanced detector, the first photodetector, the second photodetector and the third photodetector.

2. The monitoring device capable of simultaneously measuring distributed temperature and distributed sound waves according to claim 1, characterized in that: The light source adopts a single-frequency narrow-linewidth laser source.

3. The monitoring device capable of simultaneously measuring distributed temperature and distributed sound waves according to claim 1, characterized in that: The light source is a 1550nm narrow line width light source.

4. The monitoring device capable of simultaneously measuring distributed temperature and distributed sound waves according to claim 1, characterized in that: The pulse modulator is an acousto-optic modulator or an electro-optic modulator.

5. The monitoring device capable of simultaneously measuring distributed temperature and distributed sound waves according to claim 1, characterized in that: The pulse modulator and optical amplifier are replaced by SOA devices respectively.

6. The monitoring device capable of simultaneously measuring distributed temperature and distributed sound waves according to claim 1, characterized in that: The core diameter of the few-mode optical fiber is 16 μm to 33 μm.

7. The monitoring device capable of simultaneously measuring distributed temperature and distributed sound waves according to claim 1, characterized in that: The few-mode optical fiber is a two-mode, four-mode or six-mode optical fiber.

8. The monitoring device capable of simultaneously measuring distributed temperature and distributed sound waves according to claim 1, characterized in that: There are two few-mode optical fibers, namely, a reference few-mode optical fiber and a sensing few-mode optical fiber. The second port of the optical fiber multiplexer is connected to the reference few-mode optical fiber, and the reference few-mode optical fiber is connected to the sensing few-mode optical fiber.

9. The monitoring device capable of simultaneously measuring distributed temperature and distributed sound waves according to claim 1, characterized in that: The wavelength division multiplexer is used to separate the Raman signal and the Rayleigh signal in the reflected light signal of the few-mode optical fiber, the balanced detector is used to receive the Rayleigh scattering signal of the Rayleigh signal, the first photodetector receives the Rayleigh intensity signal for receiving the Rayleigh signal, and the second photodetector and the third photodetector are used to receive the Stokes light and the anti-Stokes light of the Raman signal respectively.

10. The monitoring device capable of simultaneously measuring distributed temperature and distributed sound waves according to claim 9, characterized in that: The temperature is responded by Raman signal, and the sound wave is responded by Rayleigh signal.

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