Superfine-diameter heterogeneous optical fiber hydrophone and manufacturing process thereof

Abstract

The invention discloses a superfine heterogeneous optical fiber hydrophone and a manufacturing process thereof. The hydrophone comprises a core shaft, sensitization column shells and heterogeneous optical fiber interferometers, a cavity is formed in the core shaft in a penetrating mode, the sensitization column shells are symmetrically arranged on the two sides of the core shaft, the heterogeneous optical fiber interferometers are installed in the cavity of the core shaft, and each heterogeneous optical fiber interferometer comprises a heterogeneous optical fiber coupler, a reference arm ultra-short thin-diameter optical fiber and a sensing arm ultra-thin-diameter optical fiber. The heterogeneous optical fiber coupler, the reference arm ultra-short thin-diameter optical fiber and the reference arm reflecting mirror are straightly fixed in the cavity; the sensing arm ultra-thin-diameter optical fiber is uniformly wound on the sensitization cylindrical shell, and the tail end of the sensing arm ultra-thin-diameter optical fiber is connected with the sensing arm reflecting mirror. According to the invention, the ultra-small-diameter ultra-small-mode-field optical fiber is adopted, the small-diameter small-mode-field optical fiber forms a heterogeneous optical fiber interference structure, and the optical fiber is coiled and packaged in an ultra-thin high-sensitivity structure, so that the manufacturing of the ultra-small-diameter, low-light insertion-loss and high-sensitivity hydrophone is realized, and the ultra-small-diameter, low-light insertion-loss and high-sensitivity hydrophone can be applied to the fields of underwater sound target detection, environmental noise measurement, seabed mineral resource exploration and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber acoustic sensing, and in particular relates to an ultra-fine diameter heterogeneous optical fiber hydrophone and a manufacturing process thereof. Background Art

[0002] Fiber optic hydrophone array modules are effective equipment for underwater acoustic target detection, ocean noise environment measurement, seabed mineral resource exploration, etc. They have the advantages of being passive underwater, anti-electromagnetic interference, corrosion-resistant, remotely transmittable, and easy to expand, and have been promoted and applied in many fields. With the promotion and application of small and medium-sized underwater platforms, fiber optic hydrophone arrays as platform equipment loads have become new development trends in miniaturization, lightness, low power consumption, scalability, and enhanced capabilities. Therefore, new requirements for fiber optic hydrophones such as small size, low weight, and high reliability have been put forward.

[0003] At present, both at home and abroad, fiber optic hydrophones use changes in light intensity, light phase, and light polarization to obtain water acoustic signals to achieve sensing. Among them, the light phase change transduction method is the most widespread and most stable way to obtain and restore water acoustic signals. It usually uses specific fiber optic optical path structures and devices such as fiber interferometer type, fiber FP interferometer type, and active fiber grating type to achieve this function.

[0004] The point-type fiber-optic hydrophone unit uses optical fiber wound on a sensitive organic shell structure of a specific diameter, and is connected to an optical structure such as a fiber grating pair or a fiber device group to build a fiber interferometer. The wound sensitive optical fiber forms a highly sensitive acquisition of water sound and vibration signals, which is converted into an interference signal output of optical phase changes, and is restored by photoelectric detection and demodulation. The fiber-optic hydrophone array module is a combined application of fiber-optic hydrophones, which exists in the form of linear arrays, planar arrays, and volume arrays. The diameter, thickness, bending radius, transmission distance, array element scale, array channel noise, array gain, characteristic size and specifications of the array module are all limited by the specifications and optical characteristics of the fiber-optic hydrophone, that is, there is the following implicit relationship.

[0005] Table 1 Size limitation and response factors of fiber optic hydrophone

[0006] From the analysis of the above table, we can see that the small size design of the fiber optic hydrophone is mainly limited by the fiber optic winding radius, which should target the specific technical requirements of the long-term reliability, insertion loss, and sensitivity of the fiber optic hydrophone, thereby determining the array's operating frequency, noise level, acoustic gain, and its volume and weight and other performance.

[0007] As underwater platforms require continued improvement in their hydroacoustic payload capacity to cope with the demands for longer distances, greater accuracy, and greater depth in environmental and target measurements, the payload is required to have a smaller unit weight, smaller volume, and the same or even better performance (sensitivity, noise, etc.). This can fundamentally be achieved by designing sensors with smaller sizes and better parameters.

[0008] The optical path of the fiber optic hydrophone mostly adopts the fiber interferometer structure. Either a fiber grating pair or a coupler + 2 reflectors can form interference of optical signals to extract optical phase information. At the same time, in terms of structure, the fiber optic hydrophone needs to package the grating, coupler and reflector into it to achieve the purpose of the most concise and lowest interference. Therefore, the size of the fiber optic device and the installation layout in the hydrophone structure will also limit the minimum size of its package.

[0009] The specific problems encountered in the ultra-thin diameter of optical fiber hydrophones include the following four aspects: (1) Reduced reliability of ultra-fine winding: According to the optical fiber bending microcrack growth model, as the winding diameter decreases, the microcracks will accelerate and expand, resulting in a significant shortening of the bending reliability life. The mathematical relationship can be simply described as t 寿命 ∝(1 / 10) r This is in obvious contradiction with the long-term reliability requirements of its packaging applications. Reducing the fiber diameter, increasing the fiber screening stress, and shortening the fiber winding length can all delay crack growth, but for the requirements of sensing sensitivity and multiplexing delay, the fiber length needs to be kept at a certain value; the fiber screening stress is limited by existing processes and raw materials, and it is difficult to significantly increase it in the short term. Therefore, reducing the fiber diameter is a direct and effective way to improve fiber winding. (2) Reduced sensitivity after ultra-fine winding: Based on the theory of axial static pressure-strain of cylindrical shells, the strain is proportional to the cube of the diameter ( ), is inversely proportional to the square of the thickness ( ), the ultra-thin diameter design will inevitably cause the diameter of the sensitivity enhancement structure to decrease, which can be reversely compensated by thickness. The optical fiber layer in the thin sensitivity enhancement shell also becomes an important component factor of the thickness. Therefore, the use of thinner optical fiber can reduce the thickness of a single layer, increase the number of winding turns of a single layer, and reduce the number of winding layers, thereby reducing the overall thickness of the optical fiber layer; (3) Increased insertion loss due to ultra-fine winding: When the optical fiber is wound with an ultra-small diameter, the incident angle of the optical signal transmitted in the single-mode optical fiber at the refractive index transition interface will become smaller, making it more likely to cause optical signal leakage. Therefore, a smaller mode field diameter is required to constrain the optical signal. (4) Insufficient applicability of existing processes: Ultra-fine fiber optic hydrophones use ultra-fine diameter, ultra-small mode field single-mode optical fibers. Existing fine-diameter optical fiber fusion splicing processes and equipment are not applicable, which limits the application of ultra-fine fiber optic hydrophones in testing, array formation, and other applications. Summary of the invention

[0010] In response to the problems of reliability, sensitivity, insertion loss and process applicability that need to be solved in order to achieve ultra-fine diameter fiber optic hydrophones as discussed above, the present invention proposes a fiber optic hydrophone structure with a small diameter and high sensitivity enhancement structure based on an integrated interferometer of a thin-diameter small mode field fiber-ultra-fine-diameter ultra-small mode field fiber heterogeneity. The ultra-fine-diameter optical fiber is wound on a small sensitivity enhancement shell to achieve water acoustic signal sensing sensitivity enhancement, while the thin-diameter optical fiber realizes input docking, thereby realizing an ultra-fine-diameter fiber optic hydrophone with high sensitivity, high reliability, low insertion loss and good process convenience, providing device module-level support for small space, low load and high performance sensing application scenarios.

[0011] 1. Solution design: 1. Fiber heterogeneous integrated interferometer solution: This scheme uses a long-arm difference interferometer as the basic structure of the sensing optical path. Figure 1 The conventional structure includes 1 coupler and 2 reflectors. The coupler and the reflectors are connected by the same optical fiber. The difference in the length of the two arms of the optical fiber is controlled within a dozen meters to several tens of meters to ensure that the two arms of the optical fiber can obtain the underwater acoustic signal and the reference signal respectively.

[0012] Considering that the optical fiber needs to be wound onto a specific sensitivity enhancement structure to enhance the acquisition of underwater acoustic signals, the present invention adopts a cylindrical shell as the hydrophone sensitivity enhancement structure, and optical fibers of different diameters and lengths have different reliability lifespans after being wound into coils. Figure 4 (a), such as bending under φ8mm diameter, taking 21m long optical fiber as an example, the diameter of 160μm and the diameter of 100μm will have a life of less than 1 year and more than 10 years respectively; Figure 4 In (b), the lifespan of 21m and 10m 160μm optical fibers wound into φ8mm diameter coils is expected to be less than 1 year and more than 10 years respectively. That is, using a thinner diameter optical fiber can make the coil have a long bending life, or using a shorter optical fiber length can also achieve long-term reliability, but the latter conflicts with the high sensitivity requirements of the hydrophone and is therefore abandoned. The interferometer sensor uses ultra-fine diameter optical fiber to obtain high sensitivity and high reliability after being wound into a hydrophone.

[0013] At the same time, in order to ensure that the optical signal is confined to the fiber core under a small bend in the optical fiber, that is, to ensure a smaller bending transmission light loss, an ultra-small optical fiber mode field diameter is designed, such as 5μm. Therefore, the sensing arm of the interferometer is an ultra-fine diameter, ultra-small mode field optical fiber.

[0014] When the interferometer input and output optical fibers, sensor and reference optical fibers are all made of ultra-fine diameter and ultra-small mode field optical fibers, the advantages of high sensitivity, high reliability and low optical loss of the fiber optic hydrophone are guaranteed, but the existing plugging, fusion splicing and testing technologies are not well adapted to ultra-fine optical fibers (diameter 100μm, mode field diameter 5.5μm), making it impossible to promote the application of fiber optic hydrophones in engineering. Based on this, the interferometer retains one arm as a thin-diameter small mode field optical fiber (diameter 160μm, mode field diameter 7μm), using its mature plugging, fusion splicing and other process matching.

[0015] Therefore, the interferometer is a coupler formed by fusion taper of thin-diameter small mode field fiber and ultra-fine-diameter ultra-small mode field fiber. The input and output fibers respectively contain a pair of thin-diameter small mode field fiber and ultra-fine-diameter ultra-small mode field fiber. The lengths of the two arms are retained at the output end according to the designed arm length difference, and a reflector is made at the tail end to return the optical signal. Since the excessively long reference arm fiber needs to be stored in the hydrophone structure or coiled in the insensitive area of ​​the sensitivity-enhancing shell, it will cause a slight bend in the reference arm fiber, which will increase the insertion loss of the thin-diameter fiber in the reference arm, thereby affecting the extinction ratio of the interferometer and the signal quality. Therefore, the reference arm is designed to be an ultra-short fiber length (within a few mm) or integrated with the coupler to ensure that it can be arranged straight inside the hydrophone structure to avoid micro-bending losses and failure risks. See the optical path structure. Figure 3 .

[0016] 2. Hydrophone sensor structure scheme: The hydrophone structure design fully considers the need for hydrophone thinning, acceleration noise suppression and other effects, while also taking into account the requirements for fixed installation of optical fiber devices. The optical fiber devices are all thin and short package designs. The designed hydrophone sensitivity enhancement structure is two identical organic column shells, whose diameter is determined by the thinning target, such as Φ8mm or even smaller; the shell thickness is designed to balance the hydrophone sensitivity target and the hydrostatic pressure resistance design, that is, , A balance between the relationships.

[0017] The sensitivity enhancement column shell is fixed on the metal core shaft with mirror symmetry. The metal core shaft is also designed with mirror symmetry. The fiber optic hydrophone assembly structure formed is a mirror symmetric structure of the through-axis plane and the central vertical plane. The overall packaging structure is: sensitivity enhancement column shell-core shaft-sensitivity enhancement column shell (axial left→right), sensitivity enhancement shell-core shaft (radial inside→outside), such as Figure 4 The cylindrical shell and the core shaft form a sealed air cavity. When working in a liquid environment, the acoustic impedance mismatch at the interface forms a sensitivity enhancement effect, that is, , where (ρc) water >(ρc) air , so P air < P water (where P water , P airare the sound pressure amplitudes in water and air, respectively, (ρc) water 、(ρc) air are the product of the speed of sound in water and air and the density of the medium, respectively).

[0018] When the hydrophone structure accelerates along the axial direction, the deformations generated on the sensitivity-enhancing column shells are exactly the same, with opposite phases, thus canceling each other out; while when the structure accelerates radially, the expansions and contractions of the points symmetrically on the axial plane perpendicular to the acceleration direction on each sensitivity-enhancing column shell are exactly the same in value and opposite in phase. Assuming that the structure is described in terms of a sinusoidal signal, the acceleration signal of the left sensitivity-enhancing column shell is described as: ι =A﹒ sin(wt + φ), and the acceleration signal of the right side enhanced column shell is described as:ɑ r =-A ﹒ sin(wt + φ), (where ɑ ι 、ɑ r They represent the acceleration signals obtained by the left and right column shells respectively, A is the noise signal amplitude, w is the signal frequency, t is the time, and φ is the initial phase), so they cancel each other out, thus having a good acceleration noise cancellation effect.

[0019] The core shaft is designed to be hollow at its axial center to realize fiber optic input and output; the symmetrical middle section is designed to be a cavity structure, which is mainly used to accommodate fiber optic couplers and fiber optic reflectors. In order to reduce the overall length and diameter of the hydrophone, the middle section cavity is designed to accommodate the length of a coupler and the width of the coupler and reflector arranged side by side.

[0020] 3. Fiber optic hydrophone assembly plan: The coupler in the fiber heterogeneous interferometer is encapsulated on the mounting structure of the middle cavity of the metal core shaft, and the input pigtail is led out through the hollow shaft at one end of the core shaft; the thin-diameter optical fiber of the ultra-short reference arm is laid straight, and the connected reflector is fixed in the hollow shaft at the other end of the core shaft; the ultra-fine-diameter optical fiber of the sensing arm is divided into two equal parts and wound on two sensitivity-enhancing shell structures respectively. The number of fiber layers wound on the two shells is completely symmetrical with the relative position of the windings, and the connected reflector is fixed in the middle cavity, arranged side by side with the coupler, and sealed with an outer cover to achieve device protection; the fiber outlet end and the reflector layout end of the core shaft hollow shaft core are both sealed by structure or glue to achieve the inner cavity of the core shaft. Considering the need for isolation protection such as impact resistance and corrosion resistance, after the hydrophone structure and the fiber interferometer are encapsulated, the overall encapsulation of the colloid with low water permeability is used to achieve isolation from the external environment.

[0021] Therefore, the design scheme of the present invention mainly includes three parts: the optical fiber heterogeneous integrated interferometer scheme, the hydrophone sensing structure scheme and the optical fiber hydrophone assembly scheme. The interferometer is the optical structure basis for realizing the optical fiber hydrophone. Through the unique heterogeneous design, it is suitable for winding into a coil with a smaller diameter and adapting to the packaging of a smaller structure; the sensing structure is the basis for the optical fiber hydrophone to realize the enhanced sensitivity acquisition of the water acoustic signal, and plays the role of packaging and protecting the optical fiber device, which has both ultra-fine diameter and noise suppression design; the optical fiber hydrophone assembly scheme mainly revolves around the unique packaging design of the heterogeneous interferometer and the thin-diameter enhanced sensitivity structure, ensuring the reliable and stable packaging of high-sensitivity, low-noise sensing and optical fiber devices.

[0022] Specifically, the present invention provides the following technical solutions: An ultra-fine diameter heterogeneous optical fiber hydrophone comprises a core shaft, a sensitivity enhancement column shell and a heterogeneous optical fiber interferometer, wherein a cavity is provided through the core shaft, sensitivity enhancement column shells are symmetrically provided on both sides of the core shaft, a heterogeneous optical fiber interferometer is installed in the cavity of the core shaft, and the heterogeneous optical fiber interferometer comprises a heterogeneous optical fiber coupler, the input end of the heterogeneous optical fiber coupler is respectively connected to a thin-diameter input optical fiber and an ultra-fine-diameter input optical fiber, and the output end of the heterogeneous optical fiber coupler is respectively connected to an ultra-short thin-diameter optical fiber of a reference arm and an ultra-fine-diameter optical fiber of a sensing arm. The reference arm ultra-short fine-diameter optical fiber is connected to the reference arm reflector, the sensor arm ultra-fine-diameter optical fiber is connected to the sensor arm reflector, and the heterogeneous optical fiber coupler, the reference arm ultra-short fine-diameter optical fiber and the reference arm reflector are fixed flatly in the cavity, the sensor arm ultra-fine-diameter optical fiber extends from the cavity and is evenly wound on the sensitivity-enhancing column shells on both sides, the end of the sensor arm ultra-fine-diameter optical fiber is connected to the sensor arm reflector fixed on the middle section of the cavity, a packaging box cover is provided on the middle section of the cavity, and the core shaft, the packaging box cover and the sensitivity-enhancing column shell are all provided with an external potting layer.

[0023] Furthermore, the diameter of the thin-diameter input optical fiber is greater than 120 μm, the diameter of the ultra-fine-diameter input optical fiber is less than 120 μm, the diameter of the ultra-short thin-diameter optical fiber of the reference arm is greater than 120 μm, the length of the ultra-short thin-diameter optical fiber of the reference arm is within 5 mm, the diameter of the ultra-fine-diameter optical fiber of the sensing arm is less than 120 μm, the length of the ultra-fine-diameter optical fiber of the sensing arm is 10m-30m, and the mode field of the thin-diameter input optical fiber and the ultra-short thin-diameter optical fiber of the reference arm is greater than 6.0 μm, and the mode field of the ultra-fine-diameter input optical fiber and the ultra-fine-diameter optical fiber of the sensing arm is less than 6.0 μm.

[0024] Furthermore, a middle cavity is provided in the middle section of the core shaft, both sides of the core shaft are hollow shafts, and the middle cavity is larger than the cavity of the hollow shaft and is interconnected.

[0025] Furthermore, the outer layer of the mandrel is a metal tube, and the inner layer of the mandrel is a quartz tube or a glass tube.

[0026] Furthermore, the sensitivity-enhancing column shell is composed of two sensitivity-enhancing column shell bodies which are symmetrically installed up and down, and a sensitivity-enhancing cavity is formed between the sensitivity-enhancing column shell bodies and the core shaft.

[0027] Furthermore, the core shaft and the sensitivity enhancement column shell are provided with a guide channel for the extension and winding of the ultra-fine optical fiber of the sensing arm.

[0028] Furthermore, the heterogeneous fiber coupler, the reference arm ultra-short thin-diameter optical fiber and the reference arm reflector are an integrated packaging structure.

[0029] The present invention also provides a process for manufacturing an ultra-fine diameter heterogeneous optical fiber hydrophone, comprising the following steps: S1. Make a core shaft, a sensitivity-enhancing column shell and a heterogeneous fiber interferometer respectively, wherein a cavity is horizontally provided in the core shaft, each sensitivity-enhancing column shell includes two sensitivity-enhancing column shell bodies, and the heterogeneous fiber interferometer includes a heterogeneous fiber coupler, and the input end of the heterogeneous fiber coupler is connected to the thin-diameter input fiber and the ultra-fine-diameter input fiber, and the output end of the heterogeneous fiber coupler is respectively connected to the ultra-short thin-diameter fiber of the reference arm and the ultra-fine-diameter fiber of the sensing arm, the ultra-short thin-diameter fiber of the reference arm is connected to the reference arm reflector, and the ultra-fine-diameter fiber of the sensing arm is connected to the reflector of the sensing arm; S2. Fix the sensitivity enhancement column shell on both sides of the core shaft by means of structure or gluing, so that a closed sensitivity enhancement cavity is formed between the sensitivity enhancement column shell and the core shaft; S3, fix the heterogeneous fiber coupler, the reference arm ultra-short fine-diameter fiber and the reference arm reflector in the cavity of the core shaft, wind the sensor arm ultra-fine-diameter fiber evenly on the sensitivity enhancement column shells on both sides, fix the sensor arm reflector at the end of the sensor arm ultra-fine-diameter fiber in the middle section of the cavity by structure or adhesive, and cover the packaging box cover; S4. The two ends of the cavity of the core shaft are sealed, and a colloid is used to encapsulate the outside of the fiber optic hydrophone structure to form an external potting layer to obtain a complete fiber optic hydrophone.

[0030] Furthermore, in the step S1, the heterogeneous fiber coupler, the reference arm ultra-short thin-diameter optical fiber, and the reference arm reflector are packaged into an integrated structure through colloid.

[0031] Furthermore, in step S3, the ultra-fine optical fiber of the sensing arm is marked with an equal-division point, and is laid out on one of the sensitivity-enhancing column shells along the guiding mechanism of the core axis. The fiber is wound using zero tension, and when it reaches the equal-division point, the other half of the optical fiber is guided to the other sensitivity-enhancing column shell and wound in the same manner as the symmetrical side sensitivity-enhancing column shell to form an ultra-fine optical fiber sensing coil layer.

[0032] Based on the above scheme, the beneficial effects of the present invention are: 1. High reliability and long life effect: (1) The reliability of the fiber optic hydrophone is mainly determined by the reliability of the fiber optic coil, the reliability of the device, and the overall environmental adaptability. In view of the ultra-fine diameter requirement, the present invention obtains the prediction curve of life-fiber diameter-length-coil diameter according to the fiber optic coil failure model, and designs and selects the diameter and length of the optical fiber. For example, if the fiber optic coil with a diameter of φ8mm and a length of 20m is required, a 100μm diameter optical fiber is selected to ensure a life of more than 10 years; and if the fiber optic coil with a diameter of φ8mm and a length of 10mm is required, a 160μm diameter optical fiber is selected to ensure a life of more than 10 years; at the same time, by strengthening the screening intensity control of the optical fiber, its reliability is further enhanced; based on the above, the ultra-fine diameter of the hydrophone can be matched with the long life requirement; (2) The optical fiber device adopts a thin and short sealed package, which is convenient for packaging the device in a small size structure and can also ensure the long-term reliability of the device. The mature process and the integrated interferometer device with strong screening are used, and the failure rate can be controlled at 200FITs or even less, with a long intrinsic life; (3) In terms of packaging, the hollow core shaft end seal and the overall glue potting design of the hydrophone are adopted, so that the optical fiber coil and optical fiber devices therein can be isolated from the external environment such as water and corrosive liquid, while at the same time improving the ability to resist physical damage such as impact and collision, so that its intrinsic reliability performance can be fully obtained.

[0033] 2. Low loss, low noise and high sensitivity effects: (1) Ultra-fine optical fiber adopts ultra-small mode field diameter design. For example, if the mode field diameter is below 5.5μm, based on waveguide transmission theory, it can be predicted that there is almost no light transmission mode leakage under small bends. After the process is wound around the ring, the test loss increase is within the error range of 0.5dB, achieving low optical signal loss effect; (2) The hydrophone structure consists of a core shaft, a sensitivity enhancement column shell, etc., which are all designed and packaged in a mirror image. The length of the sensitivity enhancement coil and the relative area of ​​the winding are strictly consistent. This ensures that when non-acoustic signals such as vibration are introduced, they can be completely offset regardless of whether the hydrophone is clamped at the center or at both ends. This is reflected in the acceleration sensitivity within the frequency band being generally lower than -20 dB, achieving a noise suppression effect. (3) The sensitivity of the hydrophone shell is related to its diameter, thickness, material, etc., and is cubically related to the diameter, that is, , is inversely proportional to the thickness by a square, that is, While reducing the diameter, the thickness is reduced and the matching materials are optimized, so that the ultra-fine hydrophone can still have a sensitivity similar to that of the coarse hydrophone, and a high sensitivity effect can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the structure diagram of a conventional fiber optic interferometer; Figure 1Labeling: 1-equal split ratio coupler; 2-reflector; 3-thin diameter input optical fiber; 4-reference arm thin diameter optical fiber; 5-sensing arm thin diameter optical fiber; Figure 2 It is the structure diagram of heterogeneous fiber interferometer, where: Figure 2 (a) is the structure diagram of the heterogeneous fiber interferometer with an ultra-short reference arm. Figure 2 (b) is the structural diagram of the heterogeneous fiber reference arm integrated interferometer; Figure 2 Labeling: 6-heterogeneous fiber equal splitting ratio coupler; 7-ultra-fine input fiber; 8-reference arm ultra-short fine fiber; 9-sensing arm ultra-fine fiber; 10-heterogeneous fiber reference integrated coupler; Figure 3 This is the structural diagram of the ultra-fine diameter heterogeneous optical fiber hydrophone; Figure 3 Marking instructions: 12-core shaft; 13-sensitization column shell; 14-sensitization cavity; 15-middle cavity; 16-hollow shaft; 17-left-right symmetry plane; 18-upper-lower symmetry plane; Figure 4 This is a prediction curve of optical fiber coil life and related factors, where: Figure 4 (a) is the relationship between fiber coil life-fiber diameter-winding radius. Figure 4 (b) is the relationship diagram between fiber coil life-fiber length-winding radius; Figure 5 This is the assembly process diagram of the ultra-fine diameter heterogeneous optical fiber hydrophone, where: Figure 5 (a) is a front view of the coupler fixation and ultra-fine optical fiber winding. Figure 5 (b) is a top view of the installation of the hydrophone reflector. Figure 5 (c) is a top view of the cavity package in the middle section of the hydrophone. Figure 5 (d) is a schematic diagram of the finished product of the hydrophone encapsulation; Figure 5 Labeling instructions: 19-ultra-fine diameter optical fiber sensing coil layer; 20-middle cavity packaging box cover; 21-hollow seal at the tail end of the mandrel; 22-hollow seal at the fiber entry end of the mandrel; 23-external potting layer. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with the accompanying drawings and embodiments: like Figure 1 As shown, a conventional optical fiber interferometer structure includes an equal-split ratio coupler 1, the input end of the equal-split ratio coupler 1 is connected to two thin-diameter input optical fibers 3, the output end of the equal-split ratio coupler 1 is respectively connected to a reference arm thin-diameter optical fiber 4 and a sensing arm thin-diameter optical fiber 5, the reference arm thin-diameter optical fiber 4 is connected to a reflector 2 of the reference arm, and the sensing arm thin-diameter optical fiber 5 is connected to a reflector 2 of the sensing arm.

[0036] like Figure 2 As shown, the heterogeneous fiber interferometer provided by the present invention adopts Figure 2 (a) shows a heterogeneous fiber interferometer with an ultrashort reference arm, or Figure 2 (b) shows the heterogeneous fiber reference arm integrated interferometer. Figure 2 As shown in (a) in the figure, the heterogeneous fiber interferometer of the ultra-short reference arm, the heterogeneous fiber coupler adopts a heterogeneous fiber equal-splitting light ratio coupler 6, whose input end is connected to the thin-diameter input fiber 3, and is connected to an ultra-fine-diameter input fiber 7 (as an application backup), and the output end of the heterogeneous fiber equal-splitting light ratio coupler 6 is respectively connected to the reference arm ultra-short thin-diameter fiber 8 (ultra-short length thin-diameter fiber) and the sensor arm ultra-fine-diameter fiber 9, the reference arm ultra-short thin-diameter fiber 8 is connected to the reference arm reflector 2, and the sensor arm ultra-fine-diameter fiber 9 is connected to the sensor arm reflector 2.

[0037] like Figure 2 As shown in (b), the main structure of the heterogeneous fiber reference arm integrated interferometer is consistent with the heterogeneous fiber interferometer of the ultra-short reference arm, and the difference is that the heterogeneous fiber coupler adopts the heterogeneous fiber reference integrated coupler 10, and the heterogeneous fiber reference integrated coupler 10 is slightly lengthened and thickened by the original heterogeneous fiber coupler, and the heterogeneous fiber coupler, the reference arm ultra-short thin-diameter optical fiber 8 and the reference arm reflector 2 are flatly fixed and integrally packaged by means of structure and / or colloid, thereby improving the performance and reliability of the reference arm.

[0038] like Figure 3 As shown, the present invention provides an ultra-fine diameter heterogeneous fiber optic hydrophone, including a core shaft 12, a sensitivity-enhancing column shell 13 and a heterogeneous fiber optic interferometer, wherein the core shaft 12 is mainly made of metal material, the outer layer is a metal tube, the inner layer is a quartz tube or a glass tube, a middle section of the core shaft 12 is provided with a middle section cavity 15, both sides of the core shaft 12 are hollow shafts 16, the middle section cavity 15 is larger than the cavity of the hollow shaft 16 and interconnected; two sensitivity-enhancing column shells 13 are symmetrically installed on the left and right sides of the core shaft 12, each sensitivity-enhancing column shell 13 is composed of two sensitivity-enhancing column shell bodies symmetrically installed up and down, a sensitivity-enhancing cavity 14 is formed between the sensitivity-enhancing column shell body and the core shaft 12, and the sensitivity-enhancing column shell 13 respectively achieves complete mirror symmetry with the left and right symmetry planes 17 and the upper and lower symmetry planes 18.

[0039] A heterogeneous fiber interferometer is installed in the cavity of the core shaft 12. The heterogeneous fiber coupler, the reference arm ultra-short fine-diameter fiber 8 and the reference arm reflector 2 are fixed in sequence in a straight manner on the cavity of the hollow shaft 16 on one side, the middle cavity 15 and the cavity of the hollow shaft 16 on the other side. The ultra-fine-diameter fiber 9 of the sensing arm extends from the hollow shaft 16 on one side and is evenly wound on the sensitivity-enhancing column shells 13 on both sides of the core shaft 12 to form an ultra-fine-diameter fiber sensing coil layer 19. The wound sensing coil layer 19 is mirror-imaged by the left and right symmetry planes 17 and the upper and lower symmetry planes 18, the end of the ultra-fine optical fiber 9 of the sensing arm is connected to the sensing arm reflector 2 fixed on the middle cavity 15, the hollow shafts 16 on both sides of the core shaft 12 are respectively provided with a core shaft fiber entry end hollow seal 22 and a core shaft tail end hollow seal 21, the middle cavity 15 is provided with a middle cavity packaging box cover 20, the core shaft 12, the middle cavity packaging box cover 20 and the sensitivity enhancement column shells 13 on both sides are provided with an external potting layer 23.

[0040] Furthermore, the diameter of the thin-diameter input optical fiber 3 is 160μm, the diameter of the ultra-fine-diameter input optical fiber 7 is 100μm, the diameter of the reference arm ultra-short thin-diameter optical fiber 4 is 160μm, the length of the reference arm ultra-short thin-diameter optical fiber 4 is 3mm, the diameter of the sensing arm ultra-fine-diameter optical fiber 9 is 100μm, the length of the sensing arm ultra-fine-diameter optical fiber 9 is 20m, and the mode field of the thin-diameter input optical fiber 3 and the reference arm ultra-short thin-diameter optical fiber 4 is M7μm, constituting a thin-diameter small-mode-field optical fiber, and the mode field of the ultra-fine-diameter input optical fiber 7 and the sensing arm ultra-fine-diameter optical fiber 9 is M5.5μm, constituting an ultra-fine-diameter ultra-small-mode-field optical fiber.

[0041] like Figure 5 As shown, the present invention provides a manufacturing process of an ultra-fine diameter heterogeneous optical fiber hydrophone, comprising the following steps: S1. Prepare a core shaft 12, a sensitivity enhancement column shell 13 and a heterogeneous optical fiber interferometer respectively, wherein a cavity is provided in the core shaft 12, a middle section cavity 15 is provided in the middle section of the core shaft 12, both sides of the core shaft 12 are hollow shafts 16, the middle section cavity 15 is larger than the cavity of the hollow shaft 16 and is interconnected, and each sensitivity enhancement column shell 13 includes two sensitivity enhancement column shell bodies; The heterogeneous fiber interferometer includes a heterogeneous fiber coupler, the input end of the heterogeneous fiber coupler is connected to the thin-diameter input fiber 3 and the ultra-fine-diameter input fiber 7, the output end of the heterogeneous fiber coupler is respectively connected to the reference arm ultra-short-diameter fiber 8 and the sensing arm ultra-fine-diameter fiber 9, the reference arm ultra-short-diameter fiber 8 is connected to the reference arm reflector 2, and the sensing arm ultra-fine-diameter fiber 9 is connected to the sensing arm reflector 2; S2, symmetrically install the two sensitization column shell bodies of the sensitization column shell 13 on the core shaft 12, and realize the fastening and sealing between the contact surfaces of the two by means of structure or gluing, so as to form a closed sensitization cavity 14. At this time, the two sensitization column shells respectively realize complete mirror symmetry with the left-right symmetry plane 17 and the upper-lower symmetry plane 18; S3, fix the heterogeneous fiber coupler, the reference arm ultra-short diameter fiber 8 and the reference arm reflector 2 flatly in the passage from the hollow shaft 16 of the hydrophone core shaft 12 to the middle cavity 15 to ensure the reliability of the reference arm, see Figure 5 (a); The ultra-fine optical fiber 9 of the sensing arm is marked with an equal-division point, and is laid out on one of the sensitivity-enhancing column shells 13 along the guiding mechanism of the core shaft 12. The fiber is wound using zero tension. When the equal-division point is reached, the other half of the optical fiber is guided to the other sensitivity-enhancing column shell 13, and the wire is wound in the same manner as the sensitivity-enhancing column shell 13 on the symmetrical side to form an ultra-fine optical fiber sensing coil layer 19. The wound ultra-fine optical fiber sensing coil layer 19 is mirror-imaged with the left and right symmetry planes 17 and the upper and lower symmetry planes 18, respectively. The sensing arm reflector 2 is fixed in the middle cavity 15 of the core shaft by means of structure or adhesive, see Figure 5 (b), cover the middle cavity packaging box cover 20, see Figure 5 (c); S4. Sealing protection is performed on the hollow shafts 16 at both ends of the mandrel 12. By setting a hollow seal 22 at the fiber entry end of the mandrel and a hollow seal 21 at the tail end of the mandrel, the inner and outer cavities of the mandrel 12 are isolated. Figure 5 (c) The fiber optic hydrophone structure is packaged and protected, and a low-permeability, bump-resistant colloid is used to form an external potting layer 23 to obtain a complete fiber optic hydrophone, see Figure 5 (d).

[0042] Furthermore, in step S1, Figure 2 The heterogeneous fiber reference arm integrated interferometer method shown in (b) adopts a structural and / or colloid method to flatly fix and integrally package the heterogeneous fiber coupler, the reference arm ultra-short diameter optical fiber 8 and the reference arm reflector 2, thereby improving the performance and reliability of the reference arm. At the same time, in step S3, the packaging structure is directly installed to improve the manufacturing efficiency.

[0043] Here, the product process realization, performance testing, etc. of the optical fiber hydrophone of the present invention are introduced in more detail as follows: 1. Construction of ultra-fine fiber heterogeneous interferometer: Ultra-fine fiber heterogeneous interferometer is a new type of interferometer. Figure 1Improved construction is made on the basis. Parallel fusion taper is performed using fine-diameter small mode field optical fiber such as φ160μm / M7μm optical fiber and ultra-fine-diameter ultra-small mode field optical fiber such as φ100μm / M5.5μm optical fiber, and the optical fiber coupling structure with equal splitting ratio is realized with the splitting ratio as the monitoring parameter, and the structure is subjected to miniaturized reliability packaging protection with functions such as sealing, vibration isolation, dehumidification, watertightness, and pressure resistance, and at least two layers of quartz / glass tube and metal tube are included, and the package forms a heterogeneous optical fiber coupler 6, whose input optical fiber includes a fine-diameter input optical fiber 3 and an ultra-fine-diameter input optical fiber 7, and the output end also includes a sensing arm ultra-fine-diameter optical fiber 9 for signal sensing, and the other fine-diameter optical fiber is designed as a reference arm ultra-short fine-diameter optical fiber 8, which is usually several mm long and is used for phase reference of optical interference, and a small reflector 2 is made at the end of the two output optical fibers to realize the reflection of the two optical signals to the heterogeneous optical fiber coupler 6 to form interference, and the reflector also has the same function as the coupler. Miniaturized packaging protection.

[0044] When the heterogeneous fiber coupler 6 is integrated and packaged with the reference arm reflector 2 , one independent packaging device can be reduced, and only the size of the original coupler needs to be slightly lengthened and thickened to form a heterogeneous fiber reference integrated coupler 10 .

[0045] According to the above packaging process, construct Figure 3 The input optical fiber shown includes two paths, a thin-diameter input optical fiber 3 and an ultra-fine-diameter input optical fiber 7. The heterogeneous optical fiber coupler 6 is a thin-ultra-fine fiber heterogeneous configuration. The ultra-fine-diameter optical fiber 9 of the sensing arm is an ultra-fine fiber of several tens of meters long. The ultra-short-fine-diameter optical fiber 8 of the reference arm is a thin-diameter fiber of several millimeters. The tail end integrates a heterogeneous optical fiber interferometer structure with a reflector 2.

[0046] The optical path operation is implemented as follows: light is input through the thin-diameter input optical fiber 3, and is equally divided by the heterogeneous fiber coupler 6. One path goes to the reference arm ultra-short thin-diameter optical fiber 8, and is reflected back to the heterogeneous fiber coupler 6 at the reference arm reflector 2. The other path goes to the sensor arm ultra-fine-diameter optical fiber 9, and also returns to the heterogeneous fiber coupler 6 through the sensor arm reflector 2. Through time delay matching, an optical interference signal is formed and output from the thin-diameter input optical fiber 3. The ultra-fine-diameter input optical fiber 7 is mainly used for application backup.

[0047] 2. Ultra-fine fiber optic hydrophone process realization: The two pairs of sensitivity-enhancing column shells 13 in the fiber optic hydrophone structure are installed into the structure of the core shaft 12, and the contact surfaces of the two are fastened and sealed by gluing or other means to form a closed sensitivity-enhancing cavity 14. At this time, the two sensitivity-enhancing column shells 13 respectively achieve complete mirror symmetry with the left-right symmetry plane 17 and the upper-lower symmetry plane 18.

[0048] The heterogeneous fiber coupler 6, the reference arm ultra-short diameter fiber 8 and the reference arm reflector 2 are fixed flatly in the passage from the hollow shaft 16 of the fiber hydrophone core shaft 12 to the middle cavity 15 to ensure the reliability of the reference arm 8. The ultra-fine diameter fiber 9 of the sensing arm is marked with an equal-division point, and is laid on one of the sensitivity-enhancing column shells 13 along the guiding mechanism of the core shaft 12, and is wound with zero tension. When it reaches the equal-division point, the other half of the fiber is guided to the other sensitivity-enhancing column shell 13, and the wire is wound in the same way as the symmetrical side sensitivity-enhancing column shell 13 to form an ultra-fine diameter fiber sensing coil layer 19. The wound ultra-fine diameter fiber sensing coil layer 19 is mirror-imaged with the left and right symmetry planes 17 and the upper and lower symmetry planes 18, respectively. The sensor arm reflector 2 is fixed in the middle cavity 15 of the core shaft, fixed by gluing or other methods, and the middle cavity packaging box cover 20 is covered.

[0049] The hollow shafts 16 at both ends of the mandrel 12 are sealed and protected, including the hollow seal 22 at the fiber entry end of the mandrel and the hollow seal 21 at the tail end of the mandrel, to ensure that the inner and outer cavities of the mandrel 12 are isolated. The above-mentioned optical fiber hydrophone structure is packaged and protected, and an external potting layer 23 is formed by a low-permeability, bump-resistant colloid to obtain a Figure 5 (d) The complete fiber optic hydrophone shown.

[0050] 3. Ultra-fine fiber optic hydrophone performance test: The performance test of the ultra-fine fiber hydrophone mainly tests and calibrates the overall optical insertion loss after the ring packaging, the insertion loss balance of the two arms, the optical path difference of the arm length, the sound pressure sensitivity, the acceleration sensitivity, etc. By using different test devices and systems, the thin-diameter input optical fiber 3 is connected by fusion or plugging, and the corresponding forms of optical signals (such as DC optical signals, pulse optical signals, narrow linewidth optical signals, wide spectrum optical signals, externally loaded acoustic signals, vibration signals, etc.) are input respectively, and the return optical signals are received, and different physical parameters are directly or indirectly obtained, and then the performance evaluation results of the hydrophone are obtained.

[0051] In summary, the present invention adopts a device-type fiber interferometer structure, comprehensively considers the winding reliability, low light leakage and applicable welding process / tools of thin-diameter optical fibers, and designs parallel melting and tapering of two specifications of optical fibers to form a heterogeneous coupler, so that the thin-diameter optical fiber at the input end of the coupler can be welded with mature processes, and the ultra-fine-diameter optical fiber of the sensor arm at the output end can meet the requirements of reliable, low-loss ultra-fine diameter winding. At the same time, based on the thin-diameter and anti-noise packaging structure of the hydrophone, the interferometer component is designed to be packaged in a thin and short package, and the reference arm thin-diameter optical fiber adopts an ultra-short design, and the overlap and side-by-side between the packaged components are reduced, so that the interferometer component can be installed in a smaller hydrophone structure, thereby realizing the production of an ultra-fine hydrophone.

[0052] This type of hydrophone uses ultra-fine optical fiber, so that the unit length of the sensitivity enhancement column can contain more optical fiber turns. At the same time, the thinner layer thickness has less binding force on the shell, that is, the rigidity of the shell is smaller, thus ensuring the high sensitivity of the thin-diameter optical fiber hydrophone. In addition, the hydrophone adopts a mirror design, and the sensing fiber is equally coiled on two identical sensitivity enhancement structures. The two structures are installed on the core shaft in a mirror-symmetrical manner, so that it has a good anti-acceleration noise effect.

[0053] Therefore, the ultra-fine hydrophone designed in the present invention has similar performance effects as the fine-diameter hydrophone in sensitivity, reliability, noise, insertion loss, etc. while greatly reducing the diameter size, and can well support the application in light, thin and slender sensor arrays. It is expected to greatly reduce the radial size of the linear array and break through the limitations of the aperture due to volume and weight, and enhance the application ability of the fiber-optic hydrophone system in the fields of underwater acoustic detection, underwater environmental research, and seabed mineral exploration.

[0054] It should be noted that the above embodiments are merely preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. All equivalent modifications made on the basis of the above embodiments belong to the protection scope of the present invention.

Claims

1. An ultra-fine diameter heterogeneous optical fiber hydrophone, characterized in that: The invention comprises a core shaft, a sensitivity enhancement column shell and a heterogeneous fiber interferometer, wherein a cavity is provided in the core shaft, sensitivity enhancement column shells are symmetrically provided on both sides of the core shaft, a heterogeneous fiber interferometer is installed in the cavity of the core shaft, and the heterogeneous fiber interferometer comprises a heterogeneous fiber coupler, the input end of the heterogeneous fiber coupler is respectively connected to a thin-diameter input fiber and an ultra-fine-diameter input fiber, the output end of the heterogeneous fiber coupler is respectively connected to an ultra-short-diameter fiber of a reference arm and an ultra-fine-diameter fiber of a sensing arm, and the ultra-short-diameter fiber of a reference arm is connected to an ultra-short-diameter fiber of a sensing arm. The optical fiber is connected to the reference arm reflector, the sensor arm ultra-fine diameter optical fiber is connected to the sensor arm reflector, and the heterogeneous optical fiber coupler, the reference arm ultra-short fine diameter optical fiber and the reference arm reflector are fixed flatly in the cavity, the sensor arm ultra-fine diameter optical fiber extends from the cavity and is evenly wound on the sensitivity enhancement column shells on both sides, the end of the sensor arm ultra-fine diameter optical fiber is connected to the sensor arm reflector fixed on the middle section of the cavity, a packaging box cover is provided on the middle section of the cavity, and the core shaft, the packaging box cover and the sensitivity enhancement column shell are all provided with an external potting layer.

2. The ultra-fine diameter heterogeneous optical fiber hydrophone according to claim 1, characterized in that: The diameter of the thin-diameter input optical fiber is greater than 120 μm, the diameter of the ultra-fine-diameter input optical fiber is less than 120 μm, the diameter of the ultra-short thin-diameter optical fiber of the reference arm is greater than 120 μm, the length of the ultra-short thin-diameter optical fiber of the reference arm is within 5 mm, the diameter of the ultra-fine-diameter optical fiber of the sensing arm is less than 120 μm, the length of the ultra-fine-diameter optical fiber of the sensing arm is 10m-30m, and the mode field of the thin-diameter input optical fiber and the ultra-short thin-diameter optical fiber of the reference arm is greater than 6.0 μm, and the mode field of the ultra-fine-diameter input optical fiber and the ultra-fine-diameter optical fiber of the sensing arm is less than 6.0 μm.

3. The ultra-fine diameter heterogeneous optical fiber hydrophone according to claim 1, characterized in that: The middle section of the core shaft is provided with a middle section cavity, both sides of the core shaft are hollow shafts, the middle section cavity is larger than the cavity of the hollow shaft and is interconnected.

4. The ultra-fine diameter heterogeneous optical fiber hydrophone according to claim 1, characterized in that: The outer layer of the mandrel is a metal tube, and the inner layer of the mandrel is a quartz tube or a glass tube.

5. The ultra-fine diameter heterogeneous optical fiber hydrophone according to claim 1, characterized in that: The sensitivity-enhancing column shell is composed of two sensitivity-enhancing column shell main bodies which are symmetrically installed up and down, and a sensitivity-enhancing cavity is formed between the sensitivity-enhancing column shell main bodies and the core shaft.

6. The ultra-fine diameter heterogeneous optical fiber hydrophone according to claim 1, characterized in that: The core shaft and the sensitivity-enhancing column shell are provided with a guide channel for the ultra-fine optical fiber of the sensing arm to extend and wind.

7. The ultra-fine diameter heterogeneous optical fiber hydrophone according to claim 1, characterized in that: The heterogeneous optical fiber coupler, the reference arm ultra-short thin-diameter optical fiber and the reference arm reflector are an integrated packaging structure.

8. A process for manufacturing the ultra-fine diameter heterogeneous optical fiber hydrophone according to claim 1, characterized in that: The steps include: S1. Make a core shaft, a sensitivity-enhancing column shell and a heterogeneous fiber interferometer respectively, wherein a cavity is horizontally provided in the core shaft, each sensitivity-enhancing column shell includes two sensitivity-enhancing column shell bodies, and the heterogeneous fiber interferometer includes a heterogeneous fiber coupler, and the input end of the heterogeneous fiber coupler is connected to the thin-diameter input fiber and the ultra-fine-diameter input fiber, and the output end of the heterogeneous fiber coupler is respectively connected to the ultra-short thin-diameter fiber of the reference arm and the ultra-fine-diameter fiber of the sensing arm, the ultra-short thin-diameter fiber of the reference arm is connected to the reference arm reflector, and the ultra-fine-diameter fiber of the sensing arm is connected to the reflector of the sensing arm; S2. Fix the sensitivity enhancement column shell on both sides of the core shaft by means of structure or gluing, so that a closed sensitivity enhancement cavity is formed between the sensitivity enhancement column shell and the core shaft; S3, fix the heterogeneous fiber coupler, the reference arm ultra-short fine-diameter fiber and the reference arm reflector in the cavity of the core shaft, wind the sensor arm ultra-fine-diameter fiber evenly on the sensitivity enhancement column shells on both sides, fix the sensor arm reflector at the end of the sensor arm ultra-fine-diameter fiber in the middle section of the cavity by structure or adhesive, and cover the packaging box cover; S4. The two ends of the cavity of the core shaft are sealed, and a colloid is used to encapsulate the outside of the fiber optic hydrophone structure to form an external potting layer to obtain a complete fiber optic hydrophone.

9. The manufacturing process of the ultra-fine diameter heterogeneous optical fiber hydrophone according to claim 8, characterized in that: In the step S1, the heterogeneous fiber coupler, the reference arm ultra-short thin-diameter optical fiber, and the reference arm reflector are packaged into an integrated structure through colloid.

10. The manufacturing process of the ultra-fine diameter heterogeneous optical fiber hydrophone according to claim 8, characterized in that: In step S3, the ultra-fine optical fiber of the sensing arm is marked with an equal-division point, and is laid out on one of the sensitivity-enhancing column shells along the guiding mechanism of the core axis. Zero tension fiber winding is utilized, and when the equal-division point is reached, the other half of the optical fiber is guided to the other sensitivity-enhancing column shell, and the winding is performed in the same manner as the sensitivity-enhancing column shell on the symmetrical side, thereby forming an ultra-fine optical fiber sensing coil layer.

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