Fiber optic interferometric hydrophone detection system and method

Abstract

The invention discloses an optical fiber interference hydrophone detection system and method, comprising a laser, wherein the laser emitted by the laser is transmitted to a laser isolator, the laser isolator is connected to an input end of a coupler, the other input end of the coupler is connected to a photoelectric detection module, and the photoelectric detection module is connected to a signal demodulation module; an output end of the coupler is connected to a sensor arm, and the other output end of the coupler is connected to a reference arm, the sensor arm adopts a sound-transmitting hydrophone sensor probe, and the reference arm is placed in a sound-insulating sealed box.

Description

Technical Field

[0001] The present invention belongs to the technical field of underwater target detection, and in particular relates to a fiber optic interferometric hydrophone detection system and method. Background Art

[0002] Underwater target detection and identification analysis are very important for underwater security and ocean protection. Compared with light waves, electromagnetic waves and other forms, sound waves have the least attenuation in water. Therefore, water sound detection is still the most important technical means for long-distance detection of underwater targets.

[0003] Underwater sound detection, traditional piezoelectric hydrophones are limited by their physical properties and have bottlenecks in terms of anti-electromagnetic interference, transmission distance, size and structure. In order to meet the needs of underwater anti-submarine warfare, fiber optic hydrophone technology has emerged on the basis of the development of fiber optic sensing and optoelectronic technology. Fiber optic hydrophones are different from the above-mentioned hydrophones made using electrical and magnetic principles. They are underwater sound sensors that use optical fibers as sensitive elements and information transmission. Compared with traditional hydrophones, fiber optic hydrophones have significant improvements in sensitivity, dynamic range and signal transmission. They also have many advantages such as small size, light weight and strong anti-electromagnetic interference ability.

[0004] The fiber optic hydrophones studied so far are mainly interference-type fiber optic hydrophones, and the most commonly used structures are Michelson interferometer and Mach-Zehnder structure. Although many people have proposed various detection systems for measuring water sound pressure signals, there are still some common problems, such as poor dynamic range, low sensitivity, narrow measurable frequency band, complex structure, high manufacturing process requirements and difficulty in implementation. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art and to provide a fiber optic interferometric hydrophone detection system and method; the detection system uses the fiber optic Michelson interferometer principle to perform high-precision measurements of underwater acoustic signals, and has the characteristics of strong anti-interference ability, simple structure, wide measurable frequency band, high sensitivity, simple manufacturing process, easy implementation and low cost.

[0006] The first invention of the present disclosure is to provide a fiber optic interferometric hydrophone detection system. To achieve the above purpose, the present disclosure adopts the following technical solutions:

[0007] A fiber optic interferometric hydrophone detection system comprises a laser, wherein the laser emitted by the laser is transmitted to a laser isolator, the laser isolator is connected to an input end of a coupler, the other input end of the coupler is connected to a photoelectric detection module, and the photoelectric detection module is connected to a signal demodulation module; an output end of the coupler is connected to a sensor arm, and the other output end of the coupler is connected to a reference arm, the sensor arm adopts a sound-transmitting hydrophone sensor probe, and the reference arm is placed in a sound-insulating sealed box.

[0008] As a further technical solution, the hydrophone sensor probe comprises a column, a sensing optical fiber is wound around the outside of the column, and a first optical fiber reflector is arranged at the tail end of the sensing optical fiber.

[0009] As a further technical solution, the column is a hollow structure and is made of elastic material.

[0010] As a further technical solution, the outer side of the sensing optical fiber is uniformly coated with a sound-transmitting material.

[0011] As a further technical solution, the reference arm includes a reference optical fiber, and a second optical fiber reflector is arranged at the tail end of the reference optical fiber.

[0012] As a further technical solution, the reference optical fiber is of the same length as the sensing arm.

[0013] As a further technical solution, the inside and outside of the sealed box are uniformly coated with sound insulation material.

[0014] As a further technical solution, the laser adopts a distributed feedback laser.

[0015] The second invention of the present disclosure provides a detection method of the optical fiber interferometric hydrophone detection system as described above, comprising the following steps:

[0016] The laser emits laser light, which passes through the laser isolator and coupler, and is divided into two beams by the coupler and transmitted to the sensor arm and the reference arm respectively;

[0017] The sensing arm and the reference arm both reflect the light back to the coupler to generate interference. The interference signal is transmitted to the photoelectric detection module through the coupler. The photoelectric detection module converts it into an electrical signal and transmits it to the signal demodulation module. The signal demodulation module demodulates the measured sound signal.

[0018] As a further technical solution, when the hydrophone sensor probe is affected by the sound pressure signal, the outer radius size of the column of the hydrophone sensor probe changes under the action of the sound pressure, so that the length of the sensing optical fiber changes, causing the light phase to change, thereby producing an optical path difference between the reflected light of the sensor arm and the reference arm, forming interference fringes.

[0019] The beneficial effects of the present disclosure are:

[0020] In the detection system disclosed in the present invention, the hydrophone sensor probe adopts a hollow cylindrical structure. The hollow cylinder is made of elastic material, which enhances the low-frequency response characteristics of the sensor probe, broadens the measurable frequency band range, and improves the sensitivity of the hydrophone. In addition, the outer layer of the probe is evenly coated with a composite material with good pressure resistance, water resistance and sound permeability, which improves the stability and reliability of the hydrophone.

[0021] In the detection system disclosed in the present invention, the reference arm selects a reference optical fiber of the same arm length and is placed in the same environment as the sensing arm, thereby suppressing the influence of factors such as temperature and environmental noise on the system, improving measurement accuracy and reducing the noise level of the system.

[0022] The detection system disclosed in the present invention is a system in which an optical fiber is directly wound around an elastic hollow cylinder. The cylinder directly senses external sound signals and produces deformation, which causes the strain of the optical fiber to produce an optical path difference and generate an interference signal. This improves measurement sensitivity, reduces manufacturing difficulty, and effectively reduces the manufacturing process and cost of the fiber optic hydrophone.

[0023] The detection system disclosed in the present invention utilizes a Michelson interference structure, has a simple optical path structure, is easy to build, and has low cost. At the same time, the optical path is reflected back by a reflector, and the sensitivity is doubled.

[0024] In the detection system disclosed in the present invention, a laser isolator is added to the optical path structure, which effectively avoids the influence of the reflected laser on the laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings in the specification, which constitute a part of the present application, are used to provide further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0026] Figure 1 is a schematic diagram of the overall structure of a detection system disclosed in an embodiment;

[0027] Figure 2 is a cross-sectional schematic diagram of a hydrophone sensor probe;

[0028] In the figure, 1. distributed feedback laser, 2. laser isolator, 3. 2×2 coupler, 4. elastic hollow cylinder, 5. sensing optical fiber, 6. first optical fiber reflector, 7. sealing box, 8. reference optical fiber, 9. second optical fiber reflector, 10. photoelectric detection module, 11. signal demodulation module. DETAILED DESCRIPTION

[0029] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0030] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "include" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or their combinations;

[0031] For the convenience of description, if the words "up", "down", "left" and "right" appear in the present disclosure, they only indicate that they are consistent with the up, down, left and right directions of the drawings themselves, and do not limit the structure. They are only for the convenience of describing the present disclosure and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present disclosure.

[0032] As introduced in the background technology, the existing technology has shortcomings. In order to solve the above technical problems, this application proposes a fiber optic interferometric hydrophone detection system and method, which can be used to measure water sound pressure in the fields of underwater security, underwater detection, scientific research applications, etc.

[0033] The present application provides a fiber optic interferometric hydrophone detection system, comprising a laser, wherein the laser emitted by the laser is transmitted to a laser isolator, the laser isolator is connected to an input end of a coupler, the other input end of the coupler is connected to a photoelectric detection module, and the photoelectric detection module is connected to a signal demodulation module; an output end of the coupler is connected to a sensor arm, and the other output end of the coupler is connected to a reference arm, the sensor arm adopts a sound-transmitting hydrophone sensor probe, and the reference arm is placed in a sound-insulating sealed box.

[0034] Example 1

[0035] The following is combined with Figure 1 -Attached Figure 2 The detection system disclosed in this embodiment is further described;

[0036] See attached Figure 1 As shown, the fiber optic interferometric hydrophone detection system includes a distributed feedback laser 1, a laser isolator 2, a 2×2 coupler 3, an elastic hollow cylinder 4, a sensing optical fiber 5, a first optical fiber reflector 6, a sealing box 7, a reference optical fiber 8, a second optical fiber reflector 9, a photoelectric detection module 10 and a signal demodulation module 11.

[0037] The distributed feedback laser 1 emits laser light and transmits it to the laser isolator 2. The laser isolator 2 is connected to one input end of the 2×2 coupler 3 for emitting a continuous laser signal. The photoelectric detection module 10 is connected to the other input end of the 2×2 coupler 3 for converting the detection interference signal into an electrical signal. The signal demodulation module 11 is connected to the photoelectric detection module 10 to demodulate the measured sound signal.

[0038] The laser isolator can isolate the light reflected from the through end of the 2×2 coupler, thereby avoiding affecting the laser.

[0039] The two output ends of the 2×2 coupler 3 are the sensing arm and the reference arm respectively. The hydrophone sensing probe is used as the sensing arm of the Michelson interference structure. The hydrophone sensing probe is composed of an elastic hollow cylinder 4, a sensing optical fiber 5 and a first optical fiber reflector 6. The sensing optical fiber 5 with an optical fiber reflector 6 at the tail end is evenly wound on the outer periphery of the elastic hollow cylinder 4. The outer layer of the sensing optical fiber 5 is evenly coated with a composite material with good pressure resistance, water resistance and sound permeability. Here, the existing known sound-permeable material can be used, such as polyurethane water sound-permeable material, which will not be repeated here. The elastic hollow cylinder 4 is made of elastic material. Inside the sealed box 7, a reference optical fiber 8 and a second optical fiber reflector 9 of the same length as the sensing arm form a reference arm. The reference optical fiber 8 has a second optical fiber reflector 9 at the tail end. The inside and outside of the sealed box 7 are evenly coated with a composite material with good sound insulation performance. Here, the existing known sound insulation composite material can be used, such as a polyvinyl chloride-based sound insulation composite material, which will not be repeated here.

[0040] The distributed feedback laser 1 adopts a narrow line width distributed feedback laser, and the center wavelength of the laser can be selected from 1550nm, 1480nm, 1450nm, and 1060nm. A laser with a suitable wavelength range can also be selected according to the size of the measured sound pressure signal.

[0041] Both the sensing arm and the reference arm are placed in the same underwater environment to ensure the balance between the two arms of the interferometer when there is no water acoustic pressure signal.

[0042] The sealed box 7 is acoustically isolated from the outside world and is completely insensitive to sound, ensuring that when there is a sound pressure signal, the phase change caused by the signal in the optical fiber only comes from the sensor arm, thereby improving measurement accuracy and sensitivity.

[0043] The sensing arm and the reference arm are designed to be of equal length, which can increase the sensitivity of the hydrophone and suppress the influence of temperature and environmental noise on the system.

[0044] The signal demodulation module 11 demodulates the corresponding sound pressure value from the interference signal.

[0045] When there is no underwater acoustic signal and the hydrophone sensor probe is stationary, there is no optical path difference between the two reflected lights and no interference fringes. When the hydrophone sensor probe is stretched or compressed by the underwater acoustic pressure signal, a corresponding optical path difference will occur between the two reflected lights, thus generating interference fringes.

[0046] When in use, the outside world generates water acoustic pressure signals, and the radial dimensions of the elastic hollow cylinder of the hydrophone sensor probe change under the action of sound pressure, thereby causing the length and refractive index of the sensing optical fiber wrapped around it to change, among which the change in optical fiber length is dominant, thus causing a change in the optical phase.

[0047] The radial change of the elastic hollow cylinder under the action of sound pressure can be expressed as:

[0048]

[0049] Where a is the outer radius of the thick-walled mandrel, b is the inner radius, Δa is the change in the outer radius, p is the uniform radial pressure, E is the Young's modulus of the material, and ν is the Poisson's ratio of the material. The change in the optical fiber length L caused by the change in the outer radius a of the hollow cylinder under pressure is:

[0050]

[0051] And because when light passes through an optical fiber with a length of L and a refractive index of n, the phase of the propagating light is

[0052]

[0053] Where λ is the wavelength of light in vacuum. Then the change of light phase can be expressed as a relationship related to the change of the outer radius of the hollow cylinder:

[0054]

[0055] Therefore, the water sound pressure signal is converted into the change of light phase in the sensing fiber arm, and the interference between the two arms of the interferometer produces interference fringes. The photoelectric detection module can detect the corresponding phase change in the interference fringes, and then the demodulation module can demodulate the corresponding phase change information to further obtain the measured sound signal.

[0056] The working principle of the hydrophone detection system disclosed in the present invention is:

[0057] The laser emitted by the distributed feedback laser 1 passes through the laser isolator 2 and enters the 2×2 coupler 3 to be divided into two beams of light. One of the two beams of light enters the hydrophone sensor probe as the sensing arm of the Michelson interferometer, and the other is connected to the reference optical fiber of equal arm length as the reference arm. The two beams of light are respectively incident on the fiber reflector at the end of the optical fiber, reflected on the fiber reflector, and the two beams of light reflected back to the original optical path enter the 2×2 coupler 3 to produce interference. The interference signal is output from the coupling end of the coupler and enters the photoelectric detection module, converted into an electrical signal, and finally demodulated by the demodulation module to obtain the measured sound signal.

[0058] When there is no water acoustic pressure signal and the fiber optic hydrophone sensor probe is in a stable state, there is no optical path difference between the two reflected light beams and no interference fringes.

[0059] When the fiber optic hydrophone sensor probe is affected by the sound pressure signal, the radial dimension of the outer radius of the elastic hollow cylinder in the hydrophone sensor probe changes under the action of the sound pressure, causing the length of the sensing optical fiber wrapped on it to change as well. The optical path of light in the optical fiber changes, causing the light phase to change. The reference arm is not affected by the sound pressure signal, and the optical path of light in the reference optical fiber does not change. Therefore, an optical path difference is generated between the two reflected lights, forming interference fringes with phase change information.

[0060] The interference signal coming out from the other input end of the 2×2 coupler 3 enters the photoelectric detection module 10, which can detect the corresponding phase change of the interference fringes and convert the optical signal into an electrical signal. After that, it is demodulated by the signal demodulation module 11 to obtain the corresponding phase change, and further obtain the measured water sound pressure signal.

[0061] When in use, the hydrophone sensor probe and the sealed box are placed underwater together. Because the laser irradiates the optical fiber reflector at the tail end and reflects back along the original path, the optical path change is twice the original amount. The two interference signals generate interference fringes due to the optical path difference. After detection by the photoelectric detection module, the optical signal is converted into an electrical signal, and the optical path difference is converted into the corresponding phase change information to be detected. After the signal demodulation module, the phase change information is demodulated, so the sound pressure information of the measured water is obtained. Since the optical path difference is twice the strain of the optical fiber, the sensitivity is doubled. At the same time, the sensor arm and the reference arm are in the same environment, so that the changes caused by temperature, environmental noise, etc. in the two interference arms are the same and offset each other, so the influence of the external environmental temperature on the hydrophone detection system is weakened, and the measurement accuracy and anti-interference ability are improved. Moreover, this hydrophone detection system has a simple optical path structure, simple probe process requirements, and is easy to achieve consistency, which effectively reduces the manufacturing process and cost of the optical fiber hydrophone.

[0062] Although the above describes the specific implementation methods of the present disclosure in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present disclosure. Technical personnel in the relevant field should understand that on the basis of the technical solution of the present disclosure, various modifications or variations that can be made by those skilled in the art without creative work are still within the scope of protection of the present disclosure.

[0063] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A fiber optic interferometric hydrophone detection system, characterized in that: It includes a laser, the laser emitted by the laser is transmitted to a laser isolator, the laser isolator is connected to an input end of a coupler, the other input end of the coupler is connected to a photoelectric detection module, and the photoelectric detection module is connected to a signal demodulation module; an output end of the coupler is connected to a sensor arm, and the other output end of the coupler is connected to a reference arm, the sensor arm adopts a sound-transmitting hydrophone sensor probe, and the reference arm is placed in a sound-insulating sealed box; The hydrophone sensor probe comprises a column, a sensing optical fiber is wound around the outside of the column, and a first optical fiber reflector is arranged at the tail end of the sensing optical fiber; The reference arm comprises a reference optical fiber, and a second optical fiber reflector is arranged at the tail end of the reference optical fiber; The reference optical fiber is of equal length to the sensing arm; The external world generates water sound pressure signals. The radial dimensions of the elastic hollow cylinder of the hydrophone sensor probe change under the action of sound pressure, which drives the length and refractive index of the sensor optical fiber wound on it to change. The change in the optical fiber length is dominant, causing the change in the optical phase. The hydrophone sensor probe and the sealed box are placed underwater together. The laser is irradiated to the fiber optic reflector at the tail end and then reflected back along the original path. The change in the optical path is twice the original amount.

2. The optical fiber interferometric hydrophone detection system according to claim 1, characterized in that: The column is a hollow structure and is made of elastic material.

3. The optical fiber interferometric hydrophone detection system according to claim 1, characterized in that: The outer side of the sensing optical fiber is evenly coated with a sound-transmitting material.

4. The optical fiber interferometric hydrophone detection system according to claim 1, characterized in that: The inside and outside of the sealed box are evenly coated with sound insulation material.

5. The optical fiber interferometric hydrophone detection system according to claim 1, characterized in that: The laser adopts a distributed feedback laser.

6. The detection method of the optical fiber interferometric hydrophone detection system according to any one of claims 1 to 5, characterized in that: The following steps are involved: The laser emits laser light, which passes through the laser isolator and coupler, and is divided into two beams by the coupler and transmitted to the sensor arm and the reference arm respectively; The sensing arm and the reference arm both reflect the light back to the coupler to generate interference. The interference signal is transmitted to the photoelectric detection module through the coupler. The photoelectric detection module converts it into an electrical signal and transmits it to the signal demodulation module. The signal demodulation module demodulates the measured sound signal.

7. The detection method according to claim 6, characterized in that: When the hydrophone sensor probe is affected by the sound pressure signal, the outer radius of the column of the hydrophone sensor probe changes under the action of the sound pressure, so that the length of the sensing optical fiber changes, causing the light phase to change. As a result, the reflected light of the sensing arm and the reference arm produces an optical path difference, forming interference fringes.

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