Fiber Bragg Grating Type Fiber Hydrophone with Brillouin Scattering Suppression

Abstract

The present invention provides a fiber Bragg grating type fiber hydrophone for suppressing Brillouin scattering. By connecting a tilted fiber Bragg grating between a circulator and a photodetector in the fiber Bragg grating type fiber hydrophone, one of the resonance peaks in the transmission spectrum of the tilted fiber Bragg grating corresponds stably to the stimulated Brillouin scattering wavelength in the return light, so that the stimulated Brillouin scattered light in the return light is filtered out by the tilted fiber Bragg grating, and the return light after the stimulated Brillouin scattered light is filtered out is received by the photodetector. The present invention can filter out the Brillouin scattered light transmitted backward by the fiber Bragg grating type fiber hydrophone without affecting the detection signal, reduce the phase noise of the fiber Bragg grating type fiber hydrophone, and improve the signal-to-noise ratio of the detected interference signal.

Description

Technical Field

[0001] The invention mainly relates to the technical field of optical fiber sensing and spread spectrum communication, in particular to an optical fiber grating type optical fiber hydrophone capable of suppressing Brillouin scattering. Background Art

[0002] Fiber optic hydrophones will have extremely important application prospects in the fields of underwater aquaculture and marine resource detection in the future due to their many advantages such as high sound pressure sensitivity, large dynamic range, and easy large-scale array formation. At present, fiber optic hydrophones are developing in the direction of high resolution, large scale, small size, and high reliability. The scale of sensor arrays represented by large-scale time-division, space-division, and wavelength-division hybrid multiplexing systems has gradually expanded from dozens of primitives to thousands of primitives, and the improvement of sensing range and test accuracy has also made it more concerned. At present, the two types of fiber optic hydrophones with a higher degree of practicality are the traditional fiber optic hydrophone based on Michelson interferometer (MI) and fiber grating hydrophone.

[0003] The physical essence of fiber Bragg grating is that the refractive index of the fiber core is modulated periodically, which causes coupling between different transmission modes. According to the size of the fiber Bragg grating modulation period, the core mode originally transmitted forward in the fiber core will exchange energy (couple) with the core or cladding mode transmitted forward or backward within a certain wavelength range, which will cause the transmission energy or reflection energy of the optical signal in the core to change. It is generally divided into fiber Bragg grating (FBG) and long period fiber grating (LPFG). The fiber Bragg grating mentioned in this article refers to the FBG that will cause back reflection. Fiber Bragg grating has important application value in the fields of fiber lasers, fiber sensors and fiber wavelength division multiplexing due to its strong anti-electromagnetic interference ability, large dynamic range, small size, low cost, short preparation cycle, and easy multiplexing. It also provides a new technical solution for fiber hydrophone.

[0004] Compared with the traditional fiber optic hydrophone, which needs to be used in combination with a variety of optical devices, the underwater wet-end structure of the interferometric fiber optic hydrophone based on fiber grating does not require any additional devices except the fiber grating, and a highly integrated sensor array structure can be realized on a single optical fiber. Due to its significant advantages in reliability, large scale and miniaturization, the interferometric hydrophone based on fiber grating has become a research hotspot in the fields of marine ranching, underwater environmental monitoring and seabed resource exploration in various countries in recent years.

[0005] With the continuous deepening of research on fiber-optic hydrophones, hydrophone systems are developing towards low noise and large detection range. Low noise means a small minimum detectable signal, which means that the transmission distance of the optical fiber is large. In order to ensure low system noise, fiber-optic hydrophone systems usually use high-coherence narrow-linewidth lasers as light sources. Since the threshold of stimulated Brillouin scattering of fiber lasers is proportional to the laser linewidth and inversely proportional to the fiber transmission length, the narrow linewidth and long-distance transmission characteristics of fiber-optic hydrophone systems are very likely to cause stimulated Brillouin scattering effects. In long-distance transmission systems, the stimulated Brillouin scattering effect is strong, and it will be received by the photodetector along with the interference signal light, which will increase the background noise of the system and reduce the detection performance. The existing method is to reduce the intensity of the incident laser, and then arrange the light intensity relay device at a certain length to flatten the light intensity distribution in the entire system, thereby increasing the threshold of stimulated Brillouin scattering. Although this method has increased the threshold of stimulated Brillouin scattering to a certain extent, it cannot completely solve the stimulated Brillouin scattering noise. Therefore, it is necessary to propose a method that can eliminate Brillouin scattering noise. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention proposes a fiber grating type fiber optic hydrophone capable of suppressing Brillouin scattering, which can effectively filter out stimulated Brillouin scattering noise already generated in the fiber optic hydrophone.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] A fiber grating type fiber hydrophone for suppressing Brillouin scattering includes a fiber grating type fiber hydrophone, the fiber grating type fiber hydrophone includes a pulse laser generating unit, a circulator, a sensing channel and a light return detection unit, the sensing channel is a sensing channel composed of a fiber grating, the pulse laser generating unit is used to generate a detection light signal, and input the generated detection light signal into the sensing channel through the circulator, the light return of the sensing channel is transmitted to the light return detection unit after passing through the circulator, the light return detection unit includes a tilted fiber Bragg grating and a photodetector, the transmission spectrum of the tilted fiber Bragg grating has a resonance peak consistent with the wavelength of stimulated Brillouin scattering in the light return, so that the stimulated Brillouin scattered light in the light return is filtered out by the tilted fiber Bragg grating.

[0009] Furthermore, the pulse laser generating unit comprises a laser light source and a fiber acousto-optic modulator, and the laser light emitted by the laser light source is modulated into a pulse laser by the fiber acousto-optic modulator.

[0010] Furthermore, the pulse laser generating unit also includes an optical fiber amplifier, which is used to amplify the pulse laser power.

[0011] Furthermore, the fiber grating type fiber optic hydrophone includes a fiber matching interferometer, which is connected in the optical path between the pulse laser generating unit and the circulator, or the fiber matching interferometer is connected in the optical path between the circulator and the sensing channel, or the fiber matching interferometer is connected in the optical path between the circulator and the return light detection unit.

[0012] Furthermore, the fiber-matching interferometer includes a first fiber coupler, a first transmission arm, a second transmission arm and a second fiber coupler. The laser input to the fiber-matching interferometer is divided into two beams through the first fiber coupler, one beam is transmitted to the second fiber coupler through the first transmission arm, and the other beam is transmitted to the second fiber coupler through the second transmission arm. The lengths of the first transmission arm and the second transmission arm are different, and the two beams of pulsed light with a certain time interval are combined and output through the second fiber coupler.

[0013] Furthermore, the sensing channel is a single-channel fiber Bragg grating sensing channel, a plurality of time-division-channel fiber Bragg grating sensing channels, or a plurality of wavelength-division-channel fiber Bragg grating sensing channels.

[0014] Furthermore, the tilted fiber Bragg grating is connected to a stress applying unit, which can apply different stresses to the tilted fiber Bragg grating to change the tension of the tilted fiber Bragg grating, thereby adjusting the transmission spectrum of the tilted fiber Bragg grating so that one of its resonance peaks is consistent with the stimulated Brillouin scattering wavelength in the return light, so that the stimulated Brillouin scattered light in the return light is filtered out by the tilted fiber Bragg grating.

[0015] Furthermore, both ends of the tilted fiber Bragg grating are respectively supported by fiber clamps, at least one of the two fiber clamps is connected to a displacement platform, and the relative distance between the two fiber clamps is adjusted by controlling the movement of the displacement platform, thereby adjusting the tension of the tilted fiber Bragg grating, thereby controlling the resonance peak drift of the tilted fiber Bragg grating, so that one of its resonance peaks stably corresponds to the stimulated Brillouin scattering wavelength in the return light, so that the stimulated Brillouin scattered light in the return light is filtered out by the tilted fiber Bragg grating.

[0016] Furthermore, the light return detection unit also includes a beam splitter and a spectrometer, one end of the tilted fiber Bragg grating is connected to the fiber circulator, the other end of the tilted fiber Bragg grating is connected to the beam splitter, one output end of the beam splitter is connected to the photodetector, and the other output end of the beam splitter is connected to the spectrometer, and the real-time output spectrum after the tilted fiber Bragg grating can be observed in real time through the spectrometer;

[0017] In the process of adjusting the tension of the tilted fiber Bragg grating, the relative intensity changes of the signal light and stimulated Brillouin scattering in the return light are monitored in real time, and this is used as a basis for real-time adjustment of the tension applied to the tilted fiber Bragg grating to ensure that the signal light completely passes through the tilted fiber Bragg grating and the loss of stimulated Brillouin scattering after passing through the tilted fiber Bragg grating is maximized.

[0018] Furthermore, the transmission spectrum resonance peak range of the tilted fiber Bragg grating is between 1520-1550 nm, covering the C-band wavelength range commonly used in fiber optic hydrophones.

[0019] Compared with the prior art, the technical effects of the present invention are:

[0020] 1. The present invention is based on passive optical fiber filtering devices to suppress stimulated Brillouin scattering of an optical fiber hydrophone system, and has the advantages of convenient preparation, low loss, and optical fiber compatibility.

[0021] 2. The preparation process of tilted fiber Bragg grating is simple, and the parameters such as grating period, tilt angle, resonance peak coupling depth, etc. can be flexibly adjusted according to actual needs to match different suppression wavelengths.

[0022] 3. The present invention proposes to control the drift of the resonance wavelength by stretching the tilted fiber Bragg grating, thereby preventing the resonance wavelength from being disturbed by environmental changes, thereby filtering out the instability problem of stimulated Raman scattering, and truly making the tilted fiber Bragg grating suppressing stimulated Brillouin scattering of the optical fiber hydrophone practical. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0024] Figure 1 is a schematic structural diagram of a fiber grating type fiber hydrophone for suppressing Brillouin scattering in Example 1;

[0025] Figure 2 is a schematic structural diagram of a fiber grating type fiber hydrophone for suppressing Brillouin scattering in Example 2;

[0026] Figure 3 It is a schematic structural diagram of a fiber grating type fiber hydrophone for suppressing Brillouin scattering in Example 3;

[0027] Figure 4It is a schematic structural diagram of a fiber grating type fiber hydrophone for suppressing Brillouin scattering in Example 4;

[0028] Figure 5 It is a schematic structural diagram of a fiber grating type fiber hydrophone for suppressing Brillouin scattering in Example 5;

[0029] Figure 6 It is a schematic structural diagram of a fiber grating type fiber hydrophone for suppressing Brillouin scattering in Example 6;

[0030] Figure 7 The transmission spectrum and local magnification of the tilted fiber Bragg grating, wherein (a) is the transmission spectrum of the tilted fiber Bragg grating, and (b) is the local magnification of the transmission spectrum of the tilted fiber Bragg grating;

[0031] Numbers in the figure:

[0032] 1. Pulse laser generating unit; 1-1. Laser light source; 1-2. Fiber acousto-optic modulator; 1-3. Fiber amplifier;

[0033] 2. Circulator;

[0034] 3. Sensing channel; 3-1. Fiber Bragg grating;

[0035] 4. Return light detection unit; 4-1. Tilted fiber Bragg grating; 4-2. Photoelectric detector;

[0036] 5. Fiber matching interferometer; 5-1. First fiber coupler; 5-2. First transmission arm; 5-3. Second transmission arm; 5-4. Second fiber coupler;

[0037] 6. Fiber optic clamp; 7. Fixed base; 8. Displacement platform; 9. Controller.

[0038] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] Reference Figure 1, is a structural schematic diagram of Example 1 of the present invention, which provides a fiber Bragg grating type fiber optic hydrophone for suppressing Brillouin scattering, including a pulse laser generating unit 1, a circulator 2, a sensing channel 3 and a light return detection unit 4, wherein the sensing channel 3 is a sensing channel composed of a fiber Bragg grating 3-1; the pulse laser generating unit 1 is used to generate a detection light signal, and input the generated detection light signal into the sensing channel 3 through the circulator 2, and the light return of the sensing channel 3 is transmitted to the light return detection unit 4 after passing through the circulator 2, and the light return detection unit 4 includes a tilted fiber Bragg grating 4-1 and a photodetector 4-2, and the transmission spectrum of the tilted fiber Bragg grating 4-1 has a resonance peak consistent with the wavelength of stimulated Brillouin scattering in the light return, so that the stimulated Brillouin scattered light in the light return is filtered out by the tilted fiber Bragg grating.

[0041] The optical path from the circulator 2 to the fiber Bragg grating 3-1 in the fiber Bragg grating type fiber hydrophone is usually called a transmission link. In practical applications, the transmission link often reaches tens or even hundreds of kilometers. The back Brillouin scattering generated when the light pulse passes through the optical fiber in the transmission link will also be transmitted through the circulator 2 to the tilted fiber Bragg grating 4-1. After the stimulated Brillouin scattering is transmitted to the tilted fiber Bragg grating 4-1, it will be filtered out by a resonance peak of a corresponding wavelength.

[0042] The present invention connects a tilted fiber Bragg grating between a circulator and a photodetector of a fiber Bragg grating type optical fiber hydrophone, and a certain resonance peak in the transmission spectrum of the tilted fiber Bragg grating is consistent with the wavelength of stimulated Brillouin scattering. When the stimulated Brillouin scattered light and the interference signal light reflected back from the fiber Bragg grating type optical fiber hydrophone are simultaneously transmitted to the tilted fiber Bragg grating through the circulator, the interference signal light is in the passband of the tilted fiber Bragg grating and is not affected, while the stimulated Brillouin scattered wavelength is in the stopband of the tilted fiber Bragg grating, and the power is greatly weakened, so that the stimulated Brillouin scattered light in the return light is filtered out by the tilted fiber Bragg grating. The present invention uses a tilted fiber Bragg grating to filter out the Brillouin scattered light, and can filter out the Brillouin scattered light transmitted backward from the fiber Bragg grating type optical fiber hydrophone without affecting the detected interference signal, reduce the phase noise of the fiber Bragg grating type optical fiber hydrophone, and improve the signal-to-noise ratio of the detected interference signal.

[0043] Furthermore, the transmission spectrum resonance peak range of the tilted fiber Bragg grating used in the present invention is between 1520-1550 nm, covering the C-band wavelength range commonly used in fiber optic hydrophones.

[0044] Furthermore, the tilted fiber Bragg grating of the present invention can be used to match the pre-interferometer hydrophone, the mid-interferometer hydrophone, and the post-interferometer hydrophone.

[0045] Reference Figure 2 , is a structural schematic diagram of Embodiment 2 of the present invention, providing a fiber Bragg grating type fiber hydrophone for suppressing Brillouin scattering, comprising a pulse laser generating unit 1, a circulator 2, a sensing channel 3 and a light return detection unit 4, wherein the sensing channel 3 is a sensing channel composed of a plurality of fiber Bragg gratings 3-1, and the fiber Bragg gratings 3-1 are connected by an energy transmission optical fiber. The pulse laser generating unit 1 is used to generate a detection light signal, and input the generated detection light signal into the sensing channel 3 through the circulator 2, and the light return reflected by the fiber Bragg grating 3-1 in the sensing channel 3 is transmitted to the light return detection unit 4 after passing through the circulator 2, and the light return detection unit 4 comprises a tilted fiber Bragg grating 4-1 and a photodetector 4-2, and the transmission spectrum of the tilted fiber Bragg grating 4-1 has a resonance peak consistent with the wavelength of stimulated Brillouin scattering in the light return, so that the stimulated Brillouin scattering light in the light return is filtered out by the tilted fiber Bragg grating.

[0046] The difference from Example 1 is that the tilted fiber Bragg grating 4-1 is connected to a stress applying unit, which can apply different stresses to the tilted fiber Bragg grating to change the tension of the tilted fiber Bragg grating, thereby adjusting the transmission spectrum of the tilted fiber Bragg grating so that one of its resonance peaks is consistent with the stimulated Brillouin scattering wavelength in the return light, so that the stimulated Brillouin scattered light in the return light is filtered out by the tilted fiber Bragg grating.

[0047] Reference Figure 3 , is a structural schematic diagram of Example 3 of the present invention, which provides a fiber Bragg grating type fiber optic hydrophone for suppressing Brillouin scattering, including a pulse laser generating unit 1, a circulator 2, a sensing channel 3 and a light return detection unit 4, wherein the sensing channel 3 is a sensing channel composed of a fiber Bragg grating 3-1; the pulse laser generating unit 1 is used to generate a detection light signal, and input the generated detection light signal into the sensing channel 3 through the circulator 2, and the light return of the sensing channel 3 is transmitted to the light return detection unit 4 after passing through the circulator 2, and the light return detection unit 4 includes a tilted fiber Bragg grating 4-1 and a photodetector 4-2, and the transmission spectrum of the tilted fiber Bragg grating 4-1 has a resonance peak consistent with the wavelength of stimulated Brillouin scattering in the light return, so that the stimulated Brillouin scattered light in the light return is filtered out by the tilted fiber Bragg grating.

[0048] The pulse laser generating unit 1 includes a laser light source 1-1 and a fiber acousto-optic modulator 1-2. The laser emitted by the laser light source 1-1 is modulated into a pulse laser by the fiber acousto-optic modulator 1-2. Furthermore, the pulse laser generating unit 1 also includes a fiber amplifier 1-3, which is used to amplify the pulse laser power and inject it into the fiber matching interferometer 5. Furthermore, after the laser light source 1-1 described in the present invention is emitted and adjusted by the fiber acousto-optic modulator 1-2, it can be amplified by the fiber amplifier 1-3 (such as an erbium-doped fiber amplifier), or it can be amplified without the fiber amplifier 1-3 (such as an erbium-doped fiber amplifier), depending on actual needs. The fiber grating type fiber hydrophone in this embodiment is a pre-hydrophone of the matching interferometer. The fiber matching interferometer 5 is connected in the optical path between the pulse laser generating unit 1 and the circulator 2. Furthermore, the fiber matching interferometer 5 includes a first fiber coupler 5-1, a first transmission arm 5-2, a second transmission arm 5-3 and a second fiber coupler 5-4. The laser input to the fiber matching interferometer 5 is divided into two beams through the first fiber coupler 5-1, one beam is transmitted to the second fiber coupler through the first transmission arm 5-2, and the other beam is transmitted to the second fiber coupler 5-4 through the second transmission arm 5-3. The lengths of the first transmission arm 5-2 and the second transmission arm 5-3 are different, and the two beams of pulsed light with a certain time interval are combined and output through the second fiber coupler 5-4.

[0049] The sensing channel in the present invention may be a single-channel fiber Bragg grating sensing channel, a fiber Bragg grating sensing channel with multiple time division channels, or a fiber Bragg grating sensing channel with multiple wavelength division channels.

[0050] The tilted fiber Bragg grating 4-1 is connected to a stress applying unit, which can apply different stresses to the tilted fiber Bragg grating to change the tension of the tilted fiber Bragg grating, thereby adjusting the transmission spectrum of the tilted fiber Bragg grating so that one of its resonance peaks is consistent with the stimulated Brillouin scattering wavelength in the return light, so that the stimulated Brillouin scattered light in the return light is filtered out by the tilted fiber Bragg grating.

[0051] Specifically, both ends of the tilted fiber Bragg grating 4-1 are respectively supported by fiber clamps 6, and at least one of the two fiber clamps 6 is connected to a displacement platform 8. By controlling the movement of the displacement platform 8, the relative distance between the two fiber clamps 6 is adjusted, and then the tension of the tilted fiber Bragg grating 4-1 is adjusted, so as to control the resonance peak drift of the tilted fiber Bragg grating 4-1, so that one of its resonance peaks corresponds stably to the stimulated Brillouin scattering wavelength in the return light, so that the stimulated Brillouin scattered light in the return light is filtered out by the tilted fiber Bragg grating. In this embodiment, one fiber clamp 6 is fixed on a fixed base 7, and the other fiber clamp 6 is fixed on a displacement platform 8. The structural form of the displacement platform 8 is not limited, and it can be an electric displacement platform, a manual displacement platform, etc. In this embodiment, the displacement platform is an electric displacement platform, and also includes a controller 9 for controlling the displacement amount of the electric displacement platform.

[0052] Furthermore, the return light detection unit 4 also includes a beam splitter 4-3 and a spectrometer 4-4, one end of the tilted fiber Bragg grating 4-1 is connected to the fiber circulator 2, and the other end of the tilted fiber Bragg grating 4-1 is connected to the beam splitter 4-3, and the light beam output by the tilted fiber Bragg grating 4-1 is divided into two beams by the beam splitter 4-3, one output end of the beam splitter 4-3 is connected to the photodetector 4-2, and the other output end of the beam splitter 4-3 is connected to the spectrometer 4-4, and the real-time output spectrum after the tilted fiber Bragg grating 4-1 can be observed in real time through the spectrometer 4-4;

[0053] In the process of adjusting the tension of the tilted fiber Bragg grating 4-1, the spectrometer 4-4 is used to monitor the relative intensity changes of the signal light and stimulated Brillouin scattering in the return light in real time, and this is used as a basis for real-time adjustment of the tension applied to the tilted fiber Bragg grating to ensure that the signal light completely passes through the tilted fiber Bragg grating and the loss of stimulated Brillouin scattering after passing through the tilted fiber Bragg grating is maximized.

[0054] Reference Figure 4 , is a structural schematic diagram of Example 4 of the present invention. Example 4 provides a fiber grating type fiber optic hydrophone for suppressing Brillouin scattering, which is different from Example 3 in that the fiber grating type fiber optic hydrophone in Example 4 is a hydrophone built in a matching interferometer, and the fiber matching interferometer 5 is connected in the optical path between the circulator 2 and the sensing channel 3.

[0055] Reference Figure 5, is a structural schematic diagram of Example 5 of the present invention. Example 5 provides a fiber grating type fiber optic hydrophone for suppressing Brillouin scattering, which is different from Example 3 in that the fiber grating type fiber optic hydrophone in Example 5 is a matching interferometer post-hydrophone, and the fiber matching interferometer 5 is connected in the optical path between the circulator 2 and the return light detection unit 4.

[0056] Reference Figure 6 , which is a schematic diagram of the structure of Example 6 of the present invention. Example 6 provides a fiber Bragg grating type fiber optic hydrophone for suppressing Brillouin scattering. The difference between Example 6 and Example 3 is that the fiber Bragg grating type fiber optic hydrophone in Example 6 is a multi-time division channel fiber Bragg grating hydrophone system.

[0057] Figure 7 The typical transmission spectrum and partial magnification of the tilted fiber Bragg grating used in the present invention, wherein (a) is the transmission spectrum of the tilted fiber Bragg grating, and (b) is the partial magnification of the transmission spectrum of the tilted fiber Bragg grating. The wavelength range selected in this embodiment is 1530-1550nm, covering the wavelength range commonly used in the fiber optic hydrophone system. In practical applications, the resonance peak range of the tilted fiber Bragg grating can be reasonably designed according to requirements.

[0058] Usually, the transmission link in the fiber Bragg grating type fiber optic hydrophone often reaches tens or even hundreds of kilometers. The backward Brillouin scattering generated when the light pulse passes through the transmission link will also be transmitted through the circulator in the direction of the tilted fiber Bragg grating. After the stimulated Brillouin scattering is transmitted to the tilted fiber Bragg grating, it will be filtered out by a resonance peak of the corresponding wavelength.

[0059] The fiber grating type fiber hydrophone described in the present invention can be based on phase-generated carrier modulation or a heterodyne modulation system.

[0060] The fiber grating type fiber hydrophone described in the present invention can be a single-channel hydrophone, or a fiber hydrophone system with multiple time-division channels or multiple wavelength-division channels. Multiple time-division channels refer to the same wavelength laser interrogation pulse being able to sense multiple channels, and each channel is sequentially arranged in time. Wavelength division multiplexing refers to the use of interrogation pulses of different wavelengths for sensing, each wavelength is transmitted to one or more channels, and each channel only works on one wavelength.

[0061] The present invention realizes filtering out stimulated Brillouin scattering noise in signal light in the optical fiber hydrophone, and provides important theoretical and technical support for accelerating the large-scale engineering practical application of the optical fiber hydrophone.

[0062] Matters not covered by the present invention are known technologies.

[0063] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0064] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. Fiber Bragg grating type fiber hydrophone that suppresses Brillouin scattering, It is characterized in that It includes a fiber grating type fiber optic hydrophone, which includes a pulse laser generating unit, a circulator, a sensing channel and a light return detection unit, and the sensing channel is a sensing channel composed of a fiber grating; The pulse laser generating unit is used to generate a detection light signal, and input the generated detection light signal into the sensing channel through a circulator. The return light of the sensing channel is transmitted to the return light detection unit after passing through the circulator. The return light detection unit includes a tilted fiber Bragg grating and a photodetector. The transmission spectrum of the tilted fiber Bragg grating has a resonance peak that is consistent with the stimulated Brillouin scattering wavelength in the return light, so that the stimulated Brillouin scattered light in the return light is filtered out by the tilted fiber Bragg grating. The tilted fiber Bragg grating is connected to a stress applying unit, and the stress applying unit can apply different stresses to the tilted fiber Bragg grating to change the tension of the tilted fiber Bragg grating, and control the drift of the resonance wavelength by stretching the tilted fiber Bragg grating, so as to adjust the transmission spectrum of the tilted fiber Bragg grating so that one of its resonance peaks is consistent with the stimulated Brillouin scattering wavelength in the return light, so that the stimulated Brillouin scattered light in the return light is filtered out by the tilted fiber Bragg grating. The return light detection unit also includes a beam splitter and a spectrometer, one end of the tilted fiber Bragg grating is connected to the fiber circulator, the other end of the tilted fiber Bragg grating is connected to the beam splitter, one output end of the beam splitter is connected to the photodetector, and the other output end of the beam splitter is connected to the spectrometer, and the real-time output spectrum after the tilted fiber Bragg grating can be observed in real time through the spectrometer; In the process of adjusting the tension of the tilted fiber Bragg grating, the relative intensity changes of the signal light and stimulated Brillouin scattering in the return light are monitored in real time, and this is used as a basis for real-time adjustment of the tension applied to the tilted fiber Bragg grating to ensure that the signal light completely passes through the tilted fiber Bragg grating and the loss of stimulated Brillouin scattering after passing through the tilted fiber Bragg grating is maximized.

2. The fiber Bragg grating type optical fiber hydrophone for suppressing Brillouin scattering according to claim 1, It is characterized in that The pulse laser generating unit comprises a laser light source and an optical fiber acousto-optic modulator. The laser light emitted by the laser light source is modulated into a pulse laser by the optical fiber acousto-optic modulator.

3. The fiber Bragg grating type optical fiber hydrophone for suppressing Brillouin scattering according to claim 2, It is characterized in that The pulse laser generating unit further comprises an optical fiber amplifier, which is used to amplify the power of the pulse laser.

4. The fiber Bragg grating type optical fiber hydrophone for suppressing Brillouin scattering according to claim 1, 2 or 3, It is characterized in that The fiber grating type fiber optic hydrophone includes a fiber matching interferometer, which is connected in the optical path between the pulse laser generating unit and the circulator, or in the optical path between the circulator and the sensing channel, or in the optical path between the circulator and the return light detection unit.

5. The fiber Bragg grating type optical fiber hydrophone for suppressing Brillouin scattering according to claim 4, It is characterized in that The fiber matching interferometer comprises a first fiber coupler, a first transmission arm, a second transmission arm and a second fiber coupler. The laser input to the fiber matching interferometer is divided into two beams through the first fiber coupler, one beam is transmitted to the second fiber coupler through the first transmission arm, and the other beam is transmitted to the second fiber coupler through the second transmission arm. The first transmission arm and the second transmission arm have different lengths, and the two beams of pulsed light with a certain time interval are combined and output through the second fiber coupler.

6. The fiber Bragg grating type optical fiber hydrophone for suppressing Brillouin scattering according to claim 1, 2, 3 or 5, It is characterized in that The sensing channel is a single-channel fiber Bragg grating sensing channel, a plurality of time-division-channel fiber Bragg grating sensing channels, or a plurality of wavelength-division-channel fiber Bragg grating sensing channels.

7. The fiber Bragg grating type optical fiber hydrophone for suppressing Brillouin scattering according to claim 6, It is characterized in that The two ends of the tilted fiber Bragg grating are respectively supported by fiber clamps, at least one of the two fiber clamps is connected to a displacement platform, and the relative distance between the two fiber clamps is adjusted by controlling the movement of the displacement platform, thereby adjusting the tension of the tilted fiber Bragg grating, thereby controlling the resonance peak drift of the tilted fiber Bragg grating, so that one of its resonance peaks corresponds stably to the stimulated Brillouin scattering wavelength in the return light, so that the stimulated Brillouin scattered light in the return light is filtered out by the tilted fiber Bragg grating.

8. The fiber Bragg grating type optical fiber hydrophone for suppressing Brillouin scattering according to claim 1, It is characterized in that The transmission spectrum resonance peak range of the tilted fiber Bragg grating is between 1520-1550 nm, covering the C-band wavelength range of the fiber optic hydrophone.

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