CN117288314A - Optical fiber acoustic wave sensor for simultaneously detecting transverse wave and longitudinal wave - Google Patents

Abstract

The invention discloses an optical fiber acoustic wave sensor for simultaneously detecting transverse waves and longitudinal waves, and relates to the technical field of acoustic wave detection. In the invention, a first light source and a second light source are coupled into the same optical fiber through a wavelength division multiplexer and then transmitted to a sensing unit through a circulator; the sensing unit modulates the received transverse wave signals and longitudinal wave signals to optical signals corresponding to the first light source and the second light source respectively; the modulated reflected optical signal is transmitted to a demultiplexer through a circulator; the optical signals corresponding to the first light source and the second light source are separated by the wavelength division demultiplexer; the optical signals corresponding to the first light sources after separation correspond to the transverse wave signals one by one; the optical signals corresponding to the second light sources after separation correspond to the longitudinal wave signals one by one; after the two paths of signals respectively pass through the first photoelectric detector and the second photoelectric detector, the optical signals are converted into electric signals to complete demodulation of transverse wave signals and longitudinal wave signals.

Description

A fiber optic acoustic wave sensor that simultaneously detects transverse and longitudinal waves

Technical field

The present invention relates to the technical field of acoustic wave detection, specifically an optical fiber acoustic wave sensor that simultaneously detects transverse waves and longitudinal waves.

Background technique

Sound waves are formed by the vibration of objects propagating in the medium. The forms of propagation are divided into two types. When the sound wave propagates, the vibration direction of the medium particles is consistent with the sound propagation direction, it is called a longitudinal wave; the vibration direction of the medium particles is consistent with the sound propagation direction. When vertical, it is called a transverse wave.

Because the propagation characteristics of transverse waves and longitudinal waves are different, the detection mechanisms measured by the corresponding sensors are also different. The longitudinal wave detector mainly senses changes in the longitudinal wave sound pressure through the sensing film, causing the sensing film to deform, and then converts the diaphragm deformation into an electrical signal; the shear wave detector mainly senses the shear wave through a mass block or cantilever beam structure. The acceleration changes, resulting in the strain of the cantilever beam or the displacement of the mass block, and then the cantilever beam strain or the displacement of the mass block is converted into an electrical signal.

The electronic acoustic wave sensing technology in the existing technology is relatively mature, but there are still some shortcomings, such as cable load, resonance effect of connecting cables, large low-frequency noise, poor stability and reliability; signals are susceptible to electromagnetic interference from complex external environments, Low-frequency measurement impedance matching is difficult and other issues; transverse wave sensors and longitudinal wave sensors are separated, have poor integration, low sensitivity, and large size, and cannot meet the needs of some special application environments. For example, when a pipeline leaks, the interaction between the fluid in the pipe and the pipe wall will emit longitudinal wave signals that propagate along the pipeline and shear wave signals that propagate along the pipe wall. Therefore, pipeline leakage can be monitored in real time by detecting leakage sound waves. It is difficult to install sensors in old pipelines, so the sensors are required to be highly integrated, small in size, and highly sensitive. However, existing detectors have separate transverse and longitudinal sensors. Generally, only longitudinal wave detectors are installed, which reduces the detection accuracy. . Acoustic detection can also be used for resource exploration such as oil and natural gas, natural early warning such as earthquakes and debris flows, and noise monitoring such as ships and aircraft. The measurement accuracy in the corresponding field can be effectively improved through joint detection of transverse and longitudinal waves. Therefore, it is necessary to develop high-sensitivity acoustic wave sensors that detect both transverse and longitudinal waves simultaneously.

Contents of the invention

In view of the above defects and improvement needs of the existing technology, the present invention provides an optical fiber acoustic wave sensor that simultaneously detects transverse waves and longitudinal waves, specifically including:

The sensing unit is connected to the circulator and is used to detect transverse waves and longitudinal waves at the same time. The sensing unit includes:

support plate;

Hollow eccentric optical fiber, one end of which passes through the support plate and is fixed with the support plate, and the other end is inserted into the hollow glass capillary tube to form a cantilever beam structure;

Fiber grating, engraved on one side of the fixed end of the hollow eccentric fiber;

Long period grating, engraved on the other side of the fixed end of the hollow eccentric fiber;

The sensing film is pasted on the end face of the hollow glass capillary tube;

A protective shell, fixed on the support plate, is used to protect the internal sensing structure;

The sound-transmitting hole is opened on one side of the protective shell, and the external longitudinal wave sound signal acts on the sensing film through the sound-transmitting hole;

Among them, the hollow eccentric optical fiber in the sensing unit is a cantilever beam, and the hollow glass capillary tube is a mass block. The two together form a cantilever beam structure for shear wave detection; the end face of the hollow eccentric optical fiber in the sensing unit and the sensing film form a Fabry Perot interferometer for longitudinal wave detection.

Further, the invention provides an optical fiber acoustic wave sensor that simultaneously detects transverse waves and longitudinal waves, further including:

A wavelength division multiplexer, the first input port and the second input port of which are respectively connected to the output ends of the first light source and the second light source;

A circulator, the first input port of which is connected to the output port of the wavelength division multiplexer, and the first output port of which is connected to the hollow eccentric optical fiber in the sensing unit;

A demultiplexer, the input port of which is connected to the second output port of the circulator, and the first and second output ports of which are respectively connected to the first photodetector and the second photodetector;

Among them, the wavelength division multiplexer couples lasers of different wavelengths into the same optical fiber, the circulator directionally transmits the reflected light of the sensing unit to the wavelength division multiplexer, and the wavelength division multiplexer couples the first light source and the second light source. The light emitted by the light source is separated, the first output port of the wavelength division multiplexer outputs light with the wavelength corresponding to the first light source, and the second output port of the wavelength division multiplexer outputs light with the wavelength corresponding to the second light source. The photodetector and the second photodetector respectively convert two optical signals into electrical signals. The first photodetector outputs a transverse wave signal, and the second photodetector outputs a longitudinal wave signal.

Furthermore, the hollow eccentric optical fiber and the hollow glass capillary tube form a cantilever beam structure for detecting shear wave signals;

The end face of the hollow eccentric optical fiber and the sensing film form a Fabry-Perot cavity, which is used to detect longitudinal wave signals.

Further, the fiber grating is used to sense the strain transformation of the cantilever beam, and reflect part of the light from the first light source to the demultiplexer to demodulate the shear wave signal;

The long-period grating couples the light transmitted from the first light source into the fiber grating and loses it in the cladding, thereby isolating the interference of longitudinal wave signals on transverse wave detection.

Furthermore, the hollow eccentric fiber has a cantilever beam structure, the cross-sectional area of the fiber is small, and the fiber core is close to the outer surface of the fiber. When sensing shear wave signals, the strain sensitivity is an order of magnitude higher than that of ordinary single-mode fiber, which is conducive to shear wave detection;

The core of the hollow eccentric optical fiber is facing the center of the sensing film. When the sensing film senses longitudinal wave signals, the center position has the greatest sensitivity.

Furthermore, the wall thickness of the hollow glass capillary is 30 to 100 μm, which not only serves as the mass block of the cantilever beam, but also is used to fix the sensing film.

Further, the central wavelength of the first light source is located within the corresponding bandwidth of the first input port of the wavelength division multiplexer;

The central wavelength of the second light source is located within the corresponding bandwidth of the second input port of the wavelength division multiplexer;

The central wavelength of the first light source is consistent with the central wavelength of the long period grating and is located in the middle area of the hypotenuse of the fiber grating reflection spectrum, ensuring that the sensor has high shear wave detection sensitivity.

Furthermore, the performance parameters of the wavelength division multiplexer and the demultiplexer are consistent.

Furthermore, the first output port of the circulator is connected to the hollow eccentric fiber using core-to-core fusion splicing to reduce system insertion loss.

Further, the detection range of the first photodetector includes the light waves emitted by the first light source;

The detection range of the second photodetector includes the light waves emitted by the second light source.

Compared with the existing technology, the present invention provides an optical fiber acoustic wave sensor that simultaneously detects transverse waves and longitudinal waves. Its beneficial effects are:

(1) The present invention can simultaneously sense transverse and longitudinal wave signals through the sensing unit, and convert the transverse wave signal into the strain change of the fiber grating through the cantilever beam structure composed of a hollow eccentric optical fiber and a hollow glass capillary tube. Through the end face of the hollow eccentric optical fiber and the sensing film, The constituted Fabry-Perot cavity induces longitudinal wave signals;

(2) The sensing unit of the present invention has high shear wave detection sensitivity. It uses a hollow eccentric optical fiber as a cantilever beam. The cross-sectional area of the optical fiber is greatly reduced. At the same time, the core is close to the outside of the optical fiber, making it easier to detect the cantilever caused by the shear wave signal. Strain changes at the beam root;

(3) The sensing unit of the present invention has high longitudinal wave detection sensitivity, and the material of the sensing film used is not limited. The longitudinal wave detection sensitivity of the sensor can be significantly improved by reducing the thickness of the sensing film;

(4) The sensing unit of the present invention does not contain any electrical components. The external transverse and longitudinal waves modulate optical signals. It has strong anti-electromagnetic interference ability and can be used in remote sensing and flammable and explosive application environments.

(5) The sensor of the present invention can realize simultaneous power demodulation of transverse and longitudinal wave signals through the wavelength division multiplexer and demultiplexer as well as the wave selection characteristics of fiber grating and long-period optical fiber, and the crosstalk between each other is almost zero. , high demodulation accuracy and signal-to-noise ratio higher than 50dB.

Description of drawings

Figure 1 is a schematic structural diagram of an optical fiber acoustic wave sensor that simultaneously detects transverse waves and longitudinal waves provided by the present invention;

Figure 2 is a schematic structural diagram of a sensing unit in an optical fiber acoustic wave sensor that simultaneously detects transverse waves and longitudinal waves provided by the present invention;

Figure 3 is a cross-sectional view of a hollow eccentric optical fiber in an optical fiber acoustic wave sensor that simultaneously detects transverse waves and longitudinal waves provided by the present invention;

Figure 4 is a cross-sectional view of a hollow eccentric optical fiber and a hollow glass capillary tube fixed in a fiber optic acoustic wave sensor for simultaneously detecting transverse waves and longitudinal waves provided by the present invention;

Figure 5 is a schematic diagram of the overall structure of an optical fiber acoustic wave sensor that simultaneously detects transverse waves and longitudinal waves provided by the present invention;

Figure 6 is an information flow chart of an optical fiber acoustic wave sensor that simultaneously detects transverse waves and longitudinal waves provided by the present invention.

In the figure: 1. First light source; 2. Second light source; 3. Wavelength division multiplexer; 4. Circulator; 5. Wavelength division multiplexer; 6. Sensing unit; 7. First photodetector ; 8. Second photodetector; 9. Long period grating; 10. Fiber grating; 11. Hollow eccentric optical fiber; 12. Hollow glass capillary; 13. Sensing film; 14. Support plate; 15. Protective shell; 16. Sound hole; 17. Glue.

Detailed ways

Specific embodiments of the present invention will be further described below with reference to the accompanying drawings 1 to 6 . The following examples are only used to more clearly illustrate the technical solutions of the present invention, but cannot be used to limit the scope of the present invention.

Embodiment 1: As shown in Figure 1 and Figure 6, the present invention provides an optical fiber acoustic wave sensor that simultaneously detects transverse waves and longitudinal waves, wherein:

The structural diagram of the sensing unit 6 is shown in Figure 2. The sensing unit 6 includes a long period grating 9 and a fiber grating 10, a hollow eccentric optical fiber 11, a hollow glass capillary 12, a sensing film 13, a support plate 14, a protective shell 15 and a sound-transmitting hole 16.

One end of the hollow eccentric optical fiber 11 passes through the support plate 14 and is fixed with the support plate 14, and the other end is inserted into the hollow glass capillary 12 to form a cantilever beam structure. A fiber grating 10 is engraved on the side close to the fixed end of the hollow eccentric optical fiber 11. For sensing transverse wave signals; a long-period grating 9 is engraved on the other end of the hollow eccentric optical fiber 11 to isolate the interference of longitudinal wave signals on transverse wave detection. A sensing film 13 is pasted on the end face of the hollow glass capillary tube 12, and a Fabry-Perot interferometer is formed between the end face of the hollow eccentric optical fiber 11 and the sensing film 13 for detecting longitudinal wave signals. The protective shell 15 is fixed on the support plate 14 to protect the internal sensing structure. The protective shell 15 has a sound-transmitting hole 16 on one side, and external longitudinal wave sound signals can act on the sensing film 13 through the sound-transmitting hole 16 .

Among them, the end section of the hollow glass capillary tube 12 is shown in Figure 3, with an air hole in the middle; the cladding is annular; and the core is in the annular cladding.

The hollow glass capillary tube 12 and the hollow eccentric optical fiber 11 are fixed together through glue 17. The cross-sectional view after fixation is shown in Figure 4, ensuring that the core of the hollow eccentric optical fiber 11 is near the center of the hollow glass capillary tube 12.

In this embodiment, the reflectivity corresponding to the center wavelength of the fiber grating 10 is more than 90%, and the transmittance corresponding to the center wavelength of the long period grating 9 is less than 10%, which isolates the interference of the reflected signal of the Fabry-Perot interferometer on the shear wave detection. .

In this embodiment, the distance between the hollow eccentric optical fiber 11 from the support plate 14 to the sensing film 13 is 2 to 8 cm, which ensures that the sensor detects shear wave signals with high sensitivity and has a wide frequency detection range. According to the actual measurement frequency By adjusting the length of the hollow eccentric optical fiber 11 within the range, measurement of transverse wave signals in the frequency range of 1Hz to 100kHz can be achieved.

In this embodiment, the smaller the cross-sectional area of the hollow eccentric optical fiber 11 is, the higher the shear wave detection sensitivity of the sensor is, but the higher the production cost and the greater the difficulty of production. Considering that the inner diameter of the hollow eccentric optical fiber 11 is 30-60 μm , the outer diameter is preferably 100~150μm.

In this embodiment, the diameter of the core of the hollow eccentric optical fiber 11 is 8-10 μm, which is convenient for splicing with single-mode optical fiber and has low insertion loss.

In this embodiment, the core of the hollow eccentric optical fiber 11 is near the center of the hollow glass capillary tube 12, ensuring that the core of the hollow eccentric optical fiber 11 is facing the center of the sensing film 13, so that the sensor can obtain the maximum longitudinal wave detection sensitivity, with a sensitivity of 100-200mV. /g.

In this embodiment, the wall thickness of the hollow glass capillary tube 12 is 30-100 μm, which is convenient for fixing the sensing film 13.

In this embodiment, the material of the sensing film 13 is a silicon dioxide film, which is the same material as the hollow glass capillary tube 12 and the hollow eccentric optical fiber 11 , which can effectively reduce the thermal noise of the sensor.

In this embodiment, the distance from the end face of the hollow eccentric optical fiber 11 to the sensing film 13 is 50 to 200 μm. Within this range, the Fabry-Perot interferometer has a high contrast and the sensor has high longitudinal wave detection sensitivity.

In this embodiment, the thinner the thickness of the sensing film 13, the higher the longitudinal wave detection sensitivity of the sensor. However, the detection frequency range is approximately 0.5 to 2 μm. Taking comprehensive considerations into account, the thickness of the sensing film 13 is preferably 0.5 to 2 μm, which can be determined according to actual measurements. The frequency range sets the thickness of the sensing film 13 to achieve measurement of longitudinal wave signals in the frequency range of 1Hz to 100kHz, with a sensitivity of 100 to 500mV/Pa.

In this embodiment, the support plate 14 is made of an aluminum square plate. The aluminum material is light and easy to drill holes and maintain, and facilitates the sensing unit to be fixed on the surface of the detection structure.

The structure of an optical fiber acoustic wave sensor that simultaneously detects transverse waves and longitudinal waves provided by the present invention is shown in Figure 5, including a first light source 1 and a second light source 2; a wavelength division multiplexer 3 and a demultiplexer 5; a ring 4; sensing unit 6; first photodetector 7 and second photodetector 8.

The output ends of the first light source 1 and the second light source 2 are respectively connected to the first input port and the second input port of the wavelength division multiplexer 3, and lasers of different wavelengths are coupled into the same optical fiber through the wavelength division multiplexer 3; circulator 4. Directly transmit the reflected light of the sensing unit 6 to the demultiplexer 5. The first input port of the circulator 4 is connected to the output port of the wavelength division multiplexer 3. The first output port of the circulator 4 is connected to the sensing unit. The hollow eccentric optical fiber 11 in 6, the second output port of the circulator 4 is connected to the input port of the wavelength division multiplexer 5; the wavelength division multiplexer 5 separates the light emitted by the first light source 1 and the second light source 2 Next, the first port of the wavelength division multiplexer 5 outputs the light of the corresponding wavelength of the first light source 1 and is connected with the first photodetector 7, and the second output port of the wavelength division multiplexer 5 outputs the second light source. 2 corresponds to the wavelength of light and is connected with the second photodetector 8; the first photodetector 7 and the second photodetector 8 respectively convert the two optical signals into telecommunications.

In this embodiment, the first light source 1 is a narrowband laser with a linewidth less than 1 MHz. The working center wavelength λ1 is within the working wavelength range of the first input port of the wavelength division multiplexer 3. The linewidth of the first light source 1 is much smaller than that of the optical fiber. The bandwidth of the grating 10 and the weak wavelength drift of the fiber grating 10 will cause changes in the reflected power, ensuring that the sensor has high shear wave detection sensitivity; the second light source 2 is a narrow-band laser with a line width of less than 1GHz, which ensures that the Fabry-Perot interferometer has The high contrast ratio and the working center wavelength λ2 are within the working wavelength range of the second input port of the wavelength division multiplexer 3, ensuring that the sensor has high longitudinal wave detection sensitivity.

In this embodiment, the center wavelength of the first light source 1 is basically the same as the transmission center wavelength of the long period grating 9, thereby isolating the interference of longitudinal wave signals on transverse wave detection.

In this embodiment, when the first output port of the circulator 4 is connected to the hollow eccentric optical fiber 11 of the sensing unit, a core-to-core connection is used to reduce the connection insertion loss.

In this embodiment, when no signal acts on the sensor, the reflectivity of the light emitted by the fiber grating 10 to the first light source 1 is 40 to 60%. The initial operating wavelength is located in the middle of the hypotenuse of the reflection spectrum of the fiber grating 10 to ensure that the transverse wave of the sensor is It has both greater sensitivity and greater dynamic detection range during detection.

In this embodiment, the fiber grating 10 uses a phase-shifted fiber grating. The hypotenuse of the reflection spectrum of the phase-shifted fiber grating is steeper, and the sensitivity during shear wave detection is higher, which can reach 300 to 500 mV/g.

In this embodiment, the long period grating 9 is written close to one end of the sensing film. When the sensor detects the transverse wave signal, the strain on the long period grating 9 is negligible, which ensures that the center projection wavelength of the long period grating 9 is always consistent with the first light source. 1. The central wavelengths are basically the same, completely isolating the interference of longitudinal wave signals on transverse wave detection.

In this embodiment, both the wavelength division multiplexer 3 and the demultiplexer 5 are dual-channel coarse wavelength division multiplexers, which are cheap, have small crosstalk between channels, small insertion loss, and stable performance.

The signal flow of an optical fiber acoustic wave sensor that simultaneously detects transverse waves and longitudinal waves provided by the present invention is shown in Figure 6. Both the first light source 1 and the second light source 2 are narrow-band lasers, and the corresponding center wavelengths of the emitted laser are divided into λ1 and λ2. , the laser light emitted by the first light source 1 and the second light source 2 is coupled into the same optical fiber through the wavelength division multiplexer 3, and then transmitted to the sensing unit 6 through the circulator 4. The hollow eccentric optical fiber 11 in the sensing unit 6 is a cantilever beam, and the hollow glass capillary tube 12 is a mass block. The two together form a cantilever beam structure for shear wave detection; the end face of the hollow eccentric optical fiber 11 in the sensing unit 6 is in contact with the sensing film 13 A Fabry-Perot interferometer is used for longitudinal wave detection. When transverse and longitudinal wave signals act on the sensing unit at the same time, the cantilever beam structure is only sensitive to the transverse wave signal, and the cantilever beam and the transverse wave signal vibrate synchronously, so that the fiber grating 10 is strain modulated at the corresponding frequency, thereby causing the reflection of the fiber grating 10 The spectrum undergoes periodic drift; the Fabry-Perot interferometer is only sensitive to longitudinal wave signals, and the sensing film can sense longitudinal wave signals, causing the cavity length of the Fabry-Perot interferometer to be periodically modulated, and the modulation frequency is consistent with the longitudinal wave signal. Part of the light emitted by the first light source 1 is reflected by the fiber grating 10, and the remaining light is coupled into the cladding by the long-period optical fiber 9 and lost. Therefore, the shear wave signal mainly modulates the light emitted by the first light source 1; the second light source 2 The emitted light is not within the reflection bandwidth of the fiber grating 10 and the transmission bandwidth of the long period grating 9, and can be completely transmitted to the Fabry-Perot interferometer. Therefore, the longitudinal wave signal mainly modulates the light emitted by the second light source 2. The reflected lights λ1 and λ2 modulated by the signal are transmitted to the wavelength division multiplexer 5 through the circulator 4. The wavelength division multiplexer 5 separates the light into wavelengths λ1 and λ2 and transmits them to the first light source respectively. The photodetector 7 and the second photodetector 8, the first photodetector 7 and the second photodetector 8 finally convert the optical signal into an electrical signal, the transverse wave signal output by the first photodetector 7, the second photodetector 8 outputs a longitudinal wave signal.

Taken together, the present invention provides an optical fiber acoustic wave sensor that simultaneously detects transverse waves and longitudinal waves, which has the following beneficial effects:

(1) The present invention can simultaneously sense transverse and longitudinal wave signals through the sensing unit, and convert the transverse wave signal into the strain change of the fiber grating through the cantilever beam structure composed of a hollow eccentric optical fiber and a hollow glass capillary tube. Through the end face of the hollow eccentric optical fiber and the sensing film, The constituted Fabry-Perot cavity induces longitudinal wave signals;

(2) The sensing unit of the present invention has high shear wave detection sensitivity. It uses a hollow eccentric optical fiber as a cantilever beam. The cross-sectional area of the optical fiber is greatly reduced. At the same time, the core is close to the outside of the optical fiber, making it easier to detect the cantilever caused by the shear wave signal. Strain changes at the beam root;

(3) The sensing unit of the present invention has high longitudinal wave detection sensitivity, and the material of the sensing film used is not limited. The longitudinal wave detection sensitivity of the sensor can be significantly improved by reducing the thickness of the sensing film;

(4) The sensing unit of the present invention does not contain any electrical components. The external transverse and longitudinal waves modulate optical signals. It has strong anti-electromagnetic interference ability and can be used in remote sensing and flammable and explosive application environments.

(5) The sensor of the present invention can realize simultaneous power demodulation of transverse and longitudinal wave signals through the wavelength division multiplexer and demultiplexer as well as the wave selection characteristics of fiber grating and long-period optical fiber, and the crosstalk between each other is almost zero. , high demodulation accuracy and signal-to-noise ratio higher than 50dB.

The above-described embodiments are only preferred specific implementations of the present invention, and the protection scope of the present invention is not limited thereto. Any person familiar with the art can obviously obtain simple technical solutions within the technical scope disclosed in the present invention. Changes or equivalent substitutions all fall within the protection scope of the present invention.

Claims (10)

1. An optical fiber acoustic wave sensor for simultaneously detecting transverse and longitudinal waves, comprising:

the sensing unit (6), link to each other with circulator (4) for survey transversal wave and longitudinal wave simultaneously, sensing unit (6) include:

a support plate (14);

a hollow eccentric optical fiber (11), one end of which passes through the supporting plate (14) and is fixed with the supporting plate (14), and the other end of which is inserted into the hollow glass capillary (12) to form a cantilever structure;

the optical fiber grating (10) is carved on one side of the fixed end of the hollow eccentric optical fiber (11);

a long period grating (9) carved on the other side of the fixed end of the hollow eccentric optical fiber (11);

a sensing film (13) adhered to the end face of the hollow glass capillary tube (12);

a protective shell (15) fixed on the support plate (14) for protecting the internal sensing structure;

the sound transmission hole (16) is formed in the side belt of the protective shell (15), and an external longitudinal wave sound signal acts on the sensing film (13) through the sound transmission hole (16);

the hollow eccentric optical fiber (11) in the sensing unit (6) is a cantilever beam, the hollow glass capillary (12) is a mass block, and the hollow glass capillary and the mass block form a cantilever beam structure together for transverse wave detection; the end face of the hollow eccentric optical fiber (11) in the sensing unit (6) and the sensing film (13) form a Fabry-Perot interferometer for longitudinal wave detection.

2. A fiber optic acoustic wave sensor for simultaneously detecting transverse and longitudinal waves as defined in claim 1, further comprising:

the first input port and the second input port of the wavelength division multiplexer (3) are respectively connected with the output ends of the first light source (1) and the second light source (2);

the first input port of the circulator (4) is connected with the output port of the wavelength division multiplexer (3), and the first output port of the circulator is connected with the hollow eccentric optical fiber (11) in the sensing unit (6);

the input port of the demultiplexer (5) is connected with the second output port of the circulator (4), and the first output port and the second output port of the demultiplexer are respectively connected with the first photoelectric detector (7) and the second photoelectric detector (8);

the wavelength division multiplexer (3) couples lasers with different wavelengths into the same optical fiber, the circulator (4) directionally transmits reflected light of the sensing unit (6) to the wavelength division demultiplexer (5), the wavelength division demultiplexer (5) separates light emitted by the first light source (1) and light emitted by the second light source (2), a first output port of the wavelength division demultiplexer (5) outputs light with the corresponding wavelength of the first light source (1), a second output port of the wavelength division demultiplexer (5) outputs light with the corresponding wavelength of the second light source (2), the first photoelectric detector (7) and the second photoelectric detector (8) respectively convert two paths of optical signals into electric signals, the first photoelectric detector (7) outputs transverse wave signals, and the second photoelectric detector (8) outputs longitudinal wave signals.

3. A fiber optic acoustic wave sensor for simultaneously detecting transverse and longitudinal waves as defined in claim 1, wherein:

the hollow eccentric optical fiber (11) and the hollow glass capillary (12) form a cantilever structure and are used for detecting transverse wave signals;

the end face of the hollow eccentric optical fiber (11) and the sensing film (13) form a Fabry-Perot cavity for detecting longitudinal wave signals.

4. A fiber optic acoustic wave sensor for simultaneously detecting transverse and longitudinal waves as defined in claim 2, wherein:

the fiber bragg grating (10) is used for sensing cantilever strain transformation and reflecting part of light of the first light source (1) to the wavelength division demultiplexer (5) for demodulation by transverse wave signals;

the long period grating (9) couples the light transmitted by the first light source (1) into the fiber grating (10) into the cladding for loss, and isolates the interference of the longitudinal wave signal on the transverse wave detection.

5. A fiber optic acoustic wave sensor for simultaneously detecting transverse and longitudinal waves as defined in claim 1, wherein:

the hollow eccentric optical fiber (11) is used as a cantilever structure, the cross section area of the optical fiber is small, the fiber core is close to the outer surface of the optical fiber, and when a transverse wave signal is induced, the strain sensitivity is one order of magnitude higher than that of a common single-mode optical fiber, so that transverse wave detection is facilitated;

the fiber core of the hollow eccentric optical fiber (11) is opposite to the central position of the sensing film (13), and when the sensing film (13) senses longitudinal wave signals, the sensitivity of the central position is the largest.

6. A fiber optic acoustic wave sensor for simultaneously detecting transverse and longitudinal waves as defined in claim 1, wherein:

the wall thickness of the hollow glass capillary tube (12) is 30-100 mu m, and the hollow glass capillary tube is used as a mass block of a cantilever beam and is also used for fixing a sensing film (13).

7. A fiber optic acoustic wave sensor for simultaneously detecting transverse and longitudinal waves as defined in claim 2, wherein:

the central wavelength of the first light source (1) is positioned in the bandwidth corresponding to the first input port of the wavelength division multiplexer (3);

the central wavelength of the second light source (2) is positioned in the bandwidth corresponding to the second input port of the wavelength division multiplexer (3);

the central wavelength of the first light source (1) is consistent with the central wavelength of the long period grating (9), and the first light source is positioned in the middle area of the reflection spectrum bevel edge of the fiber grating (10), so that the sensor has high transverse wave detection sensitivity.

8. A fiber optic acoustic wave sensor for simultaneously detecting transverse and longitudinal waves as defined in claim 2, wherein:

the wavelength division multiplexer (3) and the demultiplexer (5) have the same performance parameters.

9. A fiber optic acoustic wave sensor for simultaneously detecting transverse and longitudinal waves as defined in claim 2, wherein:

the first output port of the circulator (4) is connected with the hollow eccentric optical fiber (11) by adopting butt fusion, so that the insertion loss of the system is reduced.

10. A fiber optic acoustic wave sensor for simultaneously detecting transverse and longitudinal waves as defined in claim 2, wherein:

the detection range of the first photoelectric detector (7) comprises light waves emitted by the first light source (1);

the detection range of the second photodetector (8) comprises the light waves emitted by the second light source (2).