A very low frequency optical fiber hydrophone

Abstract

The present invention relates to a very low frequency optical fiber hydrophone, which includes a structural part and an optical path part. The structural part includes an upper pressing plate and a lower pressing plate, and a plurality of springs are arranged between the two. A guide column is inserted in the spring, and the lower end of the guide column is connected to a support platform, and the lower pressing plate is fixed on the support platform; a reference optical fiber is wound between the outer surfaces of the upper pressing plate and the lower pressing plate, and a measuring optical fiber is wound around the outer periphery of the support platform; the optical path part includes a sweeping laser, a photodetector, an optical fiber coupler, a measuring optical fiber, a reference optical fiber, a convex lens and a reflector. The light emitted by the sweeping laser is divided into two beams through the optical fiber coupler and enters the measuring optical fiber and the reference optical fiber respectively. The light in the measuring optical fiber is collimated and focused on the reflector through the convex lens, and returns to the optical fiber coupler along the original path after reflection. The light in the reference optical fiber is similarly reflected back to the optical fiber coupler, and the two beams of light interfere in the optical fiber coupler and are displayed through the photodetector. The device is conducive to the measurement of very low frequency signals.

Description

Technical Field

[0001] The invention relates to the field of sensors, and in particular to a very low frequency optical fiber hydrophone. Background Art

[0002] Fiber optic hydrophone is a device that uses fiber optic technology to detect underwater sound waves. It converts water sound vibrations into optical signals through highly sensitive fiber coherent measurement, and transmits them to the signal processing system through optical fiber to extract the sound signal information. It has the characteristics of anti-electromagnetic interference, high sensitivity, and good frequency response characteristics. It is mainly used for the detection of sound propagation in the marine acoustic environment, seabed acoustic characteristics, target acoustic characteristics, etc. It is an advanced detection method for marine resource exploration, seabed geological survey, submarine detection, and tsunami detection, and is an important part of sonar.

[0003] The working frequencies of the currently published sonar system documents are mostly distributed above 20Hz, but the very low frequency below 20Hz concentrates most of the energy of the target sound radiation, and the waveguide propagation of the sound signal in this frequency band has a small attenuation with distance. At the same time, in the propagation of ocean sound, the lower the frequency, the longer the propagation distance. Therefore, very low frequency hydrophones have a high research value, and it is necessary to study them based on very low frequency hydrophones to fill the gap in the current research on hydrophones in very low frequencies. Summary of the invention

[0004] The object of the present invention is to provide a very low frequency optical fiber hydrophone, which is conducive to the measurement of very low frequency signals.

[0005] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a very low frequency fiber optic hydrophone, including a structural part and an optical path part, the structural part includes an upper pressing plate and a lower pressing plate arranged opposite to each other in the upper and lower directions, a plurality of springs are arranged between the upper pressing plate and the lower pressing plate, a guide column is passed through the spring, the lower end of the guide column passes through the lower pressing plate and is connected to a support platform, and the lower pressing plate is fixed on the support platform; a measuring optical fiber of the optical path part is wound between the outer surfaces of the upper pressing plate and the lower pressing plate, and a reference optical fiber of the optical path part is wound around the outer periphery of the support platform; the optical path part includes a swept frequency laser, a photodetector, a fiber coupler, a measuring optical fiber, Reference optical fiber, convex lens and reflector, the light emitted by the frequency sweeping laser is divided into two beams of 50:50 by the optical fiber coupler, the light enters the measuring optical fiber and the reference optical fiber respectively, the light in the measuring optical fiber is collimated into parallel light by the first convex lens, and then the light is focused on the first reflector by the second convex lens, the light is reflected by the first reflector and returned to the optical fiber coupler along the original path, the light in the reference optical fiber is collimated into parallel light by the third convex lens, and then the light is focused on the second reflector by the fourth convex lens, the light is reflected by the second reflector and returned to the optical fiber coupler along the original path, the two beams of light interfere in the optical fiber coupler and are displayed by the photoelectric detector.

[0006] Furthermore, the upper pressing plate and the lower pressing plate are both plate-like structures with arc surfaces on the left and right edges, and the arc surfaces of the upper pressing plate and the lower pressing plate are arranged facing each other; the measuring optical fiber bypasses the left and right edges of the upper pressing plate and the lower pressing plate with arc surfaces.

[0007] Furthermore, the upper pressing plate and the lower pressing plate are both made of tungsten steel with a hardness of 89-95 HRA to prevent deformation due to stress.

[0008] Furthermore, a clearance fit is adopted between the spring and the guide column, and there is no friction between the two; the lower part of the guide column is a threaded rod, and the diameter of the threaded rod is smaller than the diameter of the rest of the guide column; the lower end of the guide column passes through the through hole on the lower pressure plate, and is screwed into the corresponding threaded hole on the support platform through the threaded rod, thereby fixing the lower pressure plate on the support platform.

[0009] Furthermore, four springs and guide columns are arranged between the upper pressure plate and the lower pressure plate, and the four springs and guide columns are distributed in a square shape; four through holes are opened on the lower pressure plate corresponding to the four guide columns, and the diameter of the through holes is larger than the middle diameter of the threaded rod of the guide column; four threaded holes are opened on the support platform corresponding to the four guide columns, and the middle diameter of the threaded holes matches the middle diameter of the threaded rod of the guide column.

[0010] Furthermore, the guide column is made of stainless steel, and the part of the guide column except the threaded rod is a solid cylinder.

[0011] Furthermore, a groove is provided on the upper surface of the support platform, and the measuring optical fiber passes through the groove of the support platform.

[0012] Furthermore, the measuring optical fiber and the reference optical fiber are fixed and protected by waterproof glue after being wound.

[0013] Furthermore, the measuring optical fiber and the reference optical fiber are single-mode bare optical fibers.

[0014] Compared with the prior art, the present invention has the following beneficial effects: a very low frequency fiber optic hydrophone is provided, the structural part of which can achieve a large sound pressure measurement range by using a spring as a transducer and utilizing the characteristic of a small spring stiffness coefficient; at the same time, the optical coherence vibration measurement system used in the optical path part has a very high measurement resolution, combined with the high sensitivity of the optical fiber and the characteristic of the fiber optic hydrophone having a large response to weak sound source signals, thereby realizing the measurement of very low frequency signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the structure of a very low frequency fiber optic hydrophone according to an embodiment of the present invention.

[0016] Figure 2 Schematic diagram of the structure of the guide column in the embodiment of the present invention.

[0017] Figure 3 Schematic diagram of the structure of the support platform in the embodiment of the present invention.

[0018] In the figure: 1-reference optical fiber; 2-support table; 211-groove; 212-threaded hole; 3-lower pressure plate; 4-spring; 5-upper pressure plate; 6-measuring optical fiber; 7-guide column; 711-threaded rod; 712-cylinder; 8-convex lens; 9-reflector; 10-fiber coupler; 11-photodetector; 12-sweep laser. DETAILED DESCRIPTION

[0019] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0020] It should be noted that the following detailed descriptions are exemplary 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.

[0021] 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 "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0022] like Figure 1As shown, this embodiment provides a very low frequency fiber optic hydrophone, including a structural part and an optical path part, wherein the structural part includes an upper pressing plate 5 and a lower pressing plate 3 arranged opposite to each other in the upper and lower directions, a plurality of springs 4 are arranged between the upper pressing plate 5 and the lower pressing plate 3, a guide column 7 is passed through the spring 4, the lower end of the guide column 7 passes through the lower pressing plate 3 and is connected to the support platform 2, and the lower pressing plate 3 is fixed on the support platform 2; a measuring optical fiber 6 of the optical path part is wound between the outer surfaces of the upper pressing plate 5 and the lower pressing plate 3, and a reference optical fiber 1 of the optical path part is wound around the outer periphery of the support platform 2; the optical path part includes a frequency sweeping laser 12, a photodetector 11, an optical fiber coupler 10, a measuring optical fiber 6 , reference optical fiber 1, convex lens 8 and reflector 9, the light emitted by the sweep laser 12 is divided into two beams of 50:50 by the optical fiber coupler 10, and the light enters the measuring optical fiber 6 and the reference optical fiber 1 respectively. The light in the measuring optical fiber 6 is collimated into parallel light by the first convex lens, and then focused onto the first reflector by the second convex lens, reflected by the first reflector and returned to the optical fiber coupler along the original path. The light in the reference optical fiber is collimated into parallel light by the third convex lens, and then focused onto the second reflector by the fourth convex lens, reflected by the second reflector and returned to the optical fiber coupler along the original path. The two beams of light interfere in the optical fiber coupler and are displayed by the photodetector 11.

[0023] In this embodiment, the upper pressing plate 5 and the lower pressing plate 3 are both plate-like structures with arc surfaces on the left and right edges, and the arc surfaces of the upper pressing plate 5 and the lower pressing plate 3 are arranged facing each other; the measuring optical fiber 6 passes around the left and right edges of the upper pressing plate 5 and the lower pressing plate 3 with arc surfaces.

[0024] In this embodiment, the upper pressing plate 5 and the lower pressing plate 3 are both made of tungsten steel with a hardness of 89-95 HRA to prevent deformation due to stress.

[0025] In this embodiment, the spring 4 and the guide column 7 are clearance-fitted, and there is no friction between the two. Figure 2 As shown, the lower part of the guide column 7 is a threaded rod 711, and the part of the guide column 7 other than the threaded rod 711 is a solid cylinder 712, and the diameter of the threaded rod 711 is smaller than the diameter of the remaining part 712 of the guide column. The guide column 7 is made of stainless steel. The lower end of the guide column 7 passes through the through hole on the lower pressing plate 3, and is screwed into the corresponding threaded hole on the support platform 2 through the threaded rod 711, and the lower pressing plate 3 is fixed on the support platform 2 at the same time.

[0026] In this embodiment, four springs 4 and guide columns 7 are arranged between the upper pressure plate 5 and the lower pressure plate 3, and the four springs 4 and guide columns 7 are distributed in a square shape; four through holes are opened on the lower pressure plate 3 corresponding to the four guide columns, and the diameter of the through holes is larger than the middle diameter of the threaded rod of the guide column; four threaded holes 212 are opened on the support platform 2 corresponding to the four guide columns, and the middle diameter of the threaded holes matches the middle diameter of the threaded rod of the guide column.

[0027] like Figure 3 As shown, in this embodiment, a groove 211 is provided on the upper end surface of the support platform 2, and the measuring optical fiber 6 passes through the groove 211 of the support platform 2, thereby facilitating the winding of the optical fiber.

[0028] In this embodiment, the measuring optical fiber 6 and the reference optical fiber 1 are fixed and protected by waterproof glue after being wound.

[0029] In this embodiment, the measuring optical fiber 6 and the reference optical fiber 1 are single-mode bare optical fibers.

[0030] During the manufacturing process of the very low frequency fiber optic hydrophone of this embodiment, when the measuring fiber is wound, the fiber is in a critical state of relaxation and tension, and there is no tension inside the measuring fiber at this time. When the external clamp is released, under the constraint of the fiber, the potential energy released by the spring will be stored in the fiber, and tension will be generated inside the fiber, and the spring will always be in a compressed state. During the actual operation of the fiber optic hydrophone, the external sound signal acts on the surface of the upper pressure plate of the fiber optic hydrophone, and the fiber optic hydrophone as a whole will be forced to move downward. At the same time, the upper pressure plate transmits the sound pressure signal to the spring, causing the spring to be compressed. At the same time, the measuring fiber is relatively relaxed due to the downward movement of the fiber optic hydrophone as a whole, resulting in a decrease in the tension inside the fiber, which in turn causes the length of the measuring fiber to change. The reference fiber is not affected because it is wound on a rigid support platform, so that the phase of the interference signal formed by the two changes. The interference signal transmits the sound pressure signal to the demodulation system after photoelectric conversion, converts it into an electrical signal and processes it, and finally obtains the sound pressure sensitivity of the fiber optic hydrophone through solution.

[0031] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A very low frequency fiber optic hydrophone, comprising a structural part and an optical path part, wherein the structural part comprises an upper pressing plate and a lower pressing plate arranged opposite to each other in the upper and lower directions, a plurality of springs are arranged between the upper pressing plate and the lower pressing plate, a guide column is passed through the spring, the lower end of the guide column passes through the lower pressing plate and is connected to a support platform, and the lower pressing plate is fixed on the support platform; a measuring optical fiber of the optical path part is wound between the outer surfaces of the upper pressing plate and the lower pressing plate, and a reference optical fiber of the optical path part is wound around the outer periphery of the support platform; the optical path part comprises a frequency sweeping laser, a photodetector, an optical fiber coupler, a measuring optical fiber, a reference optical fiber, a convex lens and Reflector, the light emitted by the frequency sweeping laser is divided into two beams of 50:50 by the fiber coupler, and the light enters the measuring fiber and the reference fiber respectively. The light in the measuring fiber is collimated into parallel light by the first convex lens, and then focused onto the first reflector by the second convex lens, and reflected by the first reflector and returned to the fiber coupler along the original path. The light in the reference fiber is collimated into parallel light by the third convex lens, and then focused onto the second reflector by the fourth convex lens, and reflected by the second reflector and returned to the fiber coupler along the original path. The two beams of light interfere in the fiber coupler and are displayed by the photoelectric detector.

2. A very low frequency optical fiber hydrophone according to claim 1, characterized in that: The upper pressing plate and the lower pressing plate are both plate-like structures with arc surfaces on the left and right edges, and the arc surfaces of the upper pressing plate and the lower pressing plate are arranged facing each other; the measuring optical fiber passes around the left and right edges of the upper pressing plate and the lower pressing plate with arc surfaces.

3. The very low frequency optical fiber hydrophone according to claim 1, characterized in that: The upper pressing plate and the lower pressing plate are both made of tungsten steel with a hardness of 89-95HRA to prevent deformation due to stress.

4. The very low frequency fiber optic hydrophone according to claim 1, characterized in that: The spring and the guide column are clearance-fitted, and there is no friction between the two; the lower part of the guide column is a threaded rod, and the diameter of the threaded rod is smaller than the diameter of the rest of the guide column; the lower end of the guide column passes through the through hole on the lower pressure plate, and is screwed into the corresponding threaded hole on the support platform through the threaded rod, while fixing the lower pressure plate on the support platform.

5. A very low frequency optical fiber hydrophone according to claim 4, characterized in that: Four springs and guide columns are arranged between the upper pressure plate and the lower pressure plate, and the four springs and guide columns are distributed in a square shape; four through holes are opened on the lower pressure plate corresponding to the four guide columns, and the diameter of the through holes is larger than the middle diameter of the threaded rod of the guide column; four threaded holes are opened on the support platform corresponding to the four guide columns, and the middle diameter of the threaded holes matches the middle diameter of the threaded rod of the guide column.

6. The very low frequency fiber optic hydrophone according to claim 1, characterized in that: The guide column is made of stainless steel material, and the part of the guide column except the threaded rod is a solid cylinder.

7. The very low frequency optical fiber hydrophone according to claim 1, characterized in that: The upper end surface of the support platform is provided with a groove, and the measuring optical fiber passes through the groove of the support platform.

8. The very low frequency optical fiber hydrophone according to claim 1, characterized in that: The measuring optical fiber and the reference optical fiber are fixed and protected by waterproof glue after being wound.

9. The very low frequency optical fiber hydrophone according to claim 1, characterized in that: The measuring optical fiber and the reference optical fiber are single-mode bare optical fibers.

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