Pm-level tensile compression type high-sensitivity optical fiber detector

Abstract

The invention is suitable for the technical field of sensors, and provides a pm-level tensile compression type high-sensitivity optical fiber detector which comprises a mass block and two winding mechanisms. According to the pm-level tensile compression type high-sensitivity optical fiber detector, through the arrangement of the two winding mechanisms, the detector body is free of floor noise, high in signal-to-noise ratio, high in sensitivity, high in resolution ratio, low in distortion degree, large in dynamic range, wide in frequency band, especially good in low-frequency response, good in high-frequency response, high in electromagnetic interference resistance and resistant to lightning stroke; the detection and transmission of deep ground and deep sea seismic wave effective signals take light as a carrier, are almost not influenced by electromagnetic interference, are low in optical fiber loss and are suitable for long-distance transmission, and the transmission distance can reach tens of kilometers or even farther, so that long-distance arrangement, observation and arrangement can be realized, field construction operation is facilitated, and the cost is reduced. According to the invention, seismic wave information with high signal-to-noise ratio, high fidelity and high resolution from deep ground and deep sea can be detected and collected, so that detection of deep ground and deep sea becomes true.

Description

Technical Field

[0001] The invention belongs to the technical field of sensors, and in particular relates to a PM-level tensile-compression high-sensitivity optical fiber detector. Background Art

[0002] The detection of vibrations and waves has a wide range of applications, and its significance in the detection of deep earth and deep sea is self-evident. In the detection of deep earth and deep sea, finding mineral deposits above the Moho surface has always been the goal of geophysicists. At present, one of the main methods and technical means for detecting deep earth and deep sea is seismic exploration.

[0003] The carrier of seismic exploration is seismic waves. The method of obtaining seismic waves is usually to use artificial seismic sources to generate seismic waves. At present, the energy of artificially excited seismic waves can meet this demand. However, due to the complex geological structure of deep earth and deep sea, serious heterogeneity and strong scattering of seismic waves, the deep inner seismic waves have weak reflection and low signal-to-noise ratio.

[0004] Therefore, the characteristics of seismic reflection waves from deep earth and deep sea are:

[0005] First, the reflection of seismic waves deep in the earth and deep sea is weak;

[0006] Second, as the depth increases, the frequency becomes lower and lower; this is because the basic physical property that high-frequency absorption attenuates signals more than the absorption attenuation of low-frequency signals determines the effective signal of seismic waves from deep earth and deep sea. Therefore, the energy is weak and the frequency is low.

[0007] Third, to detect the interior of deep-earth and deep-sea geological structures, the resolution must be high enough to distinguish thin strata, and high resolution requires that its high-frequency response must be high enough.

[0008] It can be seen that the requirements for detectors for deep earth and deep sea exploration are: low background noise, so that the effective seismic wave signals detected and collected have a high signal-to-noise ratio; high sensitivity, able to detect and collect weak effective seismic wave signals; wide frequency bandwidth, that is, both low-frequency response and high-frequency response must be good, so that the effective seismic wave signals detected and collected have high resolution; large dynamic range to ensure that the effective signals of strong seismic waves are not distorted, and the effective signals of weak seismic waves can be detected and collected; low distortion, so that the effective seismic wave signals detected and collected have high fidelity; strong anti-interference ability; good environmental adaptability. The seismic exploration detectors currently used are mainly electromagnetic induction moving coil detectors, which are difficult to complete deep earth and deep sea exploration. Summary of the invention

[0009] The present invention provides a PM-level tensile-compression high-sensitivity optical fiber geophone, aiming to solve the problem that the currently used seismic exploration geophones are mainly electromagnetic induction moving coil geophones, which are difficult to complete the detection of deep earth and deep sea.

[0010] The present invention is implemented as follows: a PM-level tensile-compression high-sensitivity optical fiber detector includes a mass block and two winding mechanisms;

[0011] The upper surface and the lower surface of the mass block are both fixedly connected with spring sheets, and the two winding mechanisms are respectively arranged at the other ends of the two spring sheets;

[0012] The structures of the two winding mechanisms are the same, one of which includes an elastic hollow cylinder fixedly connected to the upper surface of a spring sheet, a cylindrical bracket with an outer diameter matching its inner diameter fixedly connected to the interior of the elastic hollow cylinder, and an optical fiber winding is wound around the outer surface of the elastic hollow cylinder.

[0013] Preferably, the mass block and the two spring sheets are both circular in cross-section.

[0014] Preferably, the central axes of the mass block, the two spring sheets, the two elastic hollow cylinders, and the two cylindrical supports are all located in the same straight line.

[0015] Preferably, the cylindrical bracket is made of metal.

[0016] Preferably, the length of the cylindrical bracket is smaller than the length of the elastic hollow cylinder, and the outer end surface of the cylindrical bracket and the outer end surface of the elastic hollow cylinder are located in the same plane.

[0017] Preferably, the outer surfaces of the mass block and the two winding mechanisms are covered with a shell that is compatible with the outer contour of the structure formed by the combination of the three.

[0018] Beneficial Effects

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The invention discloses a PM-level tensile-compression type high-sensitivity optical fiber detector. By arranging two winding mechanisms, the detector body has no background noise, high signal-to-noise ratio, high sensitivity, high resolution, low distortion, large dynamic range, wide frequency band, especially good low-frequency response and high-frequency response. Meanwhile, the detector has good stability, good water resistance, corrosion resistance, good environmental adaptability, wide operating temperature range, long service life, strong anti-electromagnetic interference ability and lightning resistance. The detection and transmission of effective signals of deep-earth and deep-sea seismic waves are carried out with light as the carrier, which is almost not affected by electromagnetic interference. In addition, the optical fiber loss is low, and the detector is suitable for long-distance transmission. The transmission distance can reach tens of kilometers or even farther. Therefore, the observation arrangement can be arranged over a long distance, which is convenient for field construction operations. The detector can detect and collect seismic wave information with high signal-to-noise ratio, high fidelity and high resolution from deep earth and deep sea, making the detection of deep earth and deep sea a reality. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the cross-sectional structure of the present invention;

[0022] Figure 2 It is a schematic diagram of the external structure of the present invention;

[0023] Figure 3 Graph showing relevant experimental parameters of the vulcanized rubber material in the present invention;

[0024] Figure 4 Graph showing relevant experimental parameters of the polysulfone material in the present invention.

[0025] In the figure: 1-housing, 2-mass block, 3-spring sheet, 4-hollow cylinder, 5-cylindrical bracket, 6-optical fiber winding. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0027] See also Figure 1-3 , the present invention provides a technical solution: a PM-level tensile-compression high-sensitivity optical fiber detector, comprising a mass block 2 and two winding mechanisms;

[0028] The upper surface and the lower surface of the mass block 2 are both fixedly connected with spring sheets 3, and the two winding mechanisms are respectively arranged at the other ends of the two spring sheets 3;

[0029] The structures of the two winding mechanisms are the same. One of the winding mechanisms includes an elastic hollow cylinder 4 fixedly connected to the upper surface of a spring sheet 3. The interior of the elastic hollow cylinder 4 is fixedly connected to a cylindrical bracket 5 whose outer diameter matches its inner diameter. The outer surface of the elastic hollow cylinder 4 is wound with an optical fiber winding 6.

[0030] The cross sections of the mass block 2 and the two spring sheets 3 are both circular.

[0031] The central axes of the mass block 2, the two spring sheets 3, the two elastic hollow cylinders 4, and the two cylindrical supports 5 are all located in the same straight line.

[0032] The cylindrical support 5 is made of metal.

[0033] The length of the cylindrical bracket 5 is shorter than the length of the elastic hollow cylinder 4 , and the outer end surface of the cylindrical bracket 5 and the outer end surface of the elastic hollow cylinder 4 are located in the same plane.

[0034] The outer surfaces of the mass block 2 and the two winding mechanisms are covered with a housing 1 that matches the outer contour of the structure formed by the combination of the three.

[0035] In this embodiment, when the device is affected by external vibration, the mass block 2 vibrates with the external vibration, and the vibration acts on the spring sheet 3, so the spring sheet 3 also vibrates with the external vibration, and the vibration of the spring sheet 3 acts on the optical fiber winding 6 through the elastic hollow cylinder 4. In other words, since the vibration detected by the mass block 2 acts on the optical fiber winding 6, it causes axial deformation of the optical fiber winding 6, and the axial deformation causes radial deformation, so that the refractive index and length of the optical fiber change, so that the measured light moves, while the reference light is fixed, forming a situation where one moves and the other is fixed, resulting in a change in the phase shift of the measured light, that is, the optical phase shift of the reference light changes, and the two interfere with each other. Then, using the interference measurement technology, the change in the optical phase shift is converted into a change in light intensity, and then through optical / electrical conversion and A / D conversion, the measured seismic wave signal can be measured.

[0036] In short, when the optical fiber senses vibration, the refractive index and length of the optical fiber change, causing the phase shift of the measured light to change. The specific description is: the laser emitted by the laser is divided into two paths through the optical beam expander: one path is the reference light, which is fixed, and the other path is the measured light, which is moving. The vibration of the seismic wave acts on the mass block 2, causing the axial deformation of the elastic cylinder 4 in the optical fiber detector, and the axial deformation causes radial deformation. The optical fiber is wound on this elastic cylinder 4, causing the refractive index and length of the optical fiber to change, thus causing the phase shift of the measured light, that is, the two interfere with each other, and then using the interference measurement technology, the change of the optical phase shift is converted into a change of light intensity, and then converted into an electrical signal through an optical / electrical converter, and then converted into a digital quantity through an A / D converter, and arranged into the required data format according to the user's requirements, such as the SEG-Y format, thereby completing the detection and collection of seismic waves from deep earth and deep sea.

[0037] The present invention can obtain the high performance of the PM-level tensile-compression high-sensitivity optical fiber detector through reasonable design: high sensitivity, high signal-to-noise ratio, high resolution, low distortion, large dynamic range and wide frequency band.

[0038] The following is the calculation of relevant parameters of the M-level tensile-compression high-sensitivity optical fiber detector;

[0039] The code for the parameters of the PM-level tensile-compression high-sensitivity optical fiber detector is as follows: M is the mass block, m is the optical fiber winding, D is the diameter of the optical fiber winding, N is the number of turns of the optical fiber winding, H is the height of the optical fiber winding, n is the optical fiber refractive index, σf is the Poisson's ratio of the optical fiber, Ef is the Young's modulus of the optical fiber, λ0 is the incident wavelength, p11 and p12 are the optical fiber elastic coefficients, Rin is the inner radius of the optical fiber winding, Rout is the outer radius of the optical fiber winding, σ is the Poisson's ratio of the elastic hollow cylinder, E is the Young's modulus of the elastic hollow cylinder, and α is the acceleration. The relevant mathematical expressions are as follows:

[0040] Kfn is the fiber stiffness coefficient:

[0041]

[0042] Keff is the effective stiffness coefficient of the elastic hollow cylinder:

[0043]

[0044] X is the constraint coefficient of the elastic hollow cylinder:

[0045]

[0046] Displacement sensitivity:

[0047]

[0048] The above mathematical expressions show that: under the same conditions, the displacement sensitivity of the fiber optic detector is proportional to the fiber optic winding diameter and the number of turns, and inversely proportional to the fiber optic winding height.

[0049] Acceleration sensitivity:

[0050]

[0051] Ideally, if the deformation caused by the fiber winding wrapped around the elastic hollow cylinder is ignored, the kinematic formula shows that: due to the vibration, the acceleration force causes the elastic hollow cylinder to deform, and the optical fiber is passively deformed accordingly, causing the refractive index and length of the optical fiber to change, causing the measured signal light to produce a phase shift. Under the same wavelength and optical fiber conditions, the sensitivity is related to H and M.

[0052] The sensitivity of a fiber winding when subjected to vibration acceleration forces:

[0053]

[0054] Sensitivity of PM-level stretch-compression high-sensitivity fiber optic detector: Due to the use of a stretch-compression structure, when the mass block moves downward, the fiber optic winding below is compressed, while the fiber optic winding above is stretched. Conversely, when the mass block moves upward, the fiber optic winding below is stretched, while the fiber optic winding above is compressed. Therefore, no matter whether the mass block moves upward or downward, the elastic cylinder will be axially deformed, and the axial deformation will cause radial deformation. The optical fiber is wound on this elastic cylinder, so the refractive index and length of the optical fiber change, resulting in a phase shift of the measured light. Therefore, no matter whether the mass block moves upward or downward, that is, whether the fiber optic winding is stretched or compressed, the entire fiber optic winding is doing work, and the efficiency is doubled. It can be seen that the sensitivity of this stretch-compression fiber optic detector is improved compared with a single fiber winding.

[0055] The sensitivity of the entire fiber winding of the tension-compression fiber detector when subjected to vibration acceleration:

[0056]

[0057] It can be seen that the sensitivity of the PM-level tension-compression optical fiber detector is improved. Under the same conditions, the sensitivity is increased from ~1m / 3~ of a fiber winding to ~2m / 3~, which exceeds the usual detectors, including but not limited to ordinary optical fiber sensors, MEMS detectors, piezoelectric detectors, and electromagnetic induction dynamic detectors. Only PM-level tension-compression high-sensitivity optical fiber detectors with such a tension-compression structure principle can detect seismic wave signals from deep earth and deep sea. This is the key to detecting seismic waves in deep earth and deep sea, and it is also the core technology of this patent, so that the original seismic wave information detected and collected from deep earth and deep sea has high signal-to-noise ratio, high fidelity, and high resolution.

[0058] As mentioned above, the working principle of the PM-level tensile-compression high-sensitivity fiber optic detector for measuring seismic waves is that, driven by the mass block, the fiber optic winding undergoes axial deformation, and the axial deformation causes radial deformation, thereby changing the refractive index and length of the fiber optic cable, causing a phase shift in the measured signal light, which is expressed in rad radians.

[0059] The calculation is as follows: For example, if the wavelength of the selected laser is 1550nm, then the phase of 2π radians corresponds to 1550nm, that is, 2π<=>1550nm. Assume that the height of the fiber winding is 2cm, the diameter is 4cm, and the number of turns is 400. The compression or stretching of the mass block causes the axial deformation of the fiber winding → height change → radial deformation → diameter change → circumference change → fiber length change → measured signal light phase shift. The change in the circumference of the fiber winding is 2π times the change in its height, that is: if the height changes by 1nm, the circumference changes by 2πnm. The number of turns of the fiber winding is 400, then 2π×400=2512nm, and the phase corresponding to 2512nm is 10rad radians. At present, a light phase shift of 0.1rad radians can be measured. As before, a height change of 1nm produces a corresponding phase shift of 10rad radians, and the height change corresponding to a phase shift of 0.1rad radians is 0.01nm, that is, 10pm. That is to say, the pm-level tension-compression high-sensitivity optical fiber detector can measure the vibration amplitude of seismic waves with a particle vibration displacement of 10pm. Please note that this is only the capability of the lower half or upper half of an optical fiber winding. As before, under the same conditions, due to the use of a tension-compression structure, its sensitivity is increased from ~1m / 3~ of the lower half or upper half of an optical fiber winding to ~2m / 3~.

[0060] The experimental parameters of PM-level tensile-compression high-sensitivity optical fiber detector are shown in the attached Figure 3 , Attachment Figure 4 shown.

[0061] Laser: The most basic problem of measurement is accuracy. The essence of PM-level tensile-compression high-sensitivity fiber optic detectors for detecting and measuring seismic waves from deep earth and deep sea is to use lasers of a specific wavelength as a "ruler" to measure the vibration amplitude of seismic waves. If the "ruler" itself is not accurate, the measurement result will not be accurate, so a high-precision, high-stability, ultra-narrow linewidth, low phase noise, and continuous laser emission laser must be used.

[0062] Mass block 2: Made of metal, the material selection requirements are alloy materials with high density, high specific gravity, corrosion resistance, oxidation resistance and stable performance.

[0063] Spring sheet 3: The spring sheet is made of an alloy material with good elasticity and stable performance.

[0064] Elastic material hollow cylinder 4: The selection requirements of elastic material are high-quality silicone rubber synthetic materials with appropriate hardness and softness, good elasticity, corrosion resistance, aging resistance, strong shear resistance, and especially little change under the influence of temperature and stable performance. Vulcanized silicone rubber and polysulfone PSF can be selected.

[0065] Cylindrical bracket 5: To have sufficient rigidity while reducing weight, an alloy material with light weight, good rigidity and stable performance is selected.

[0066] The shape, size, weight, elastic coefficient of the spring sheet, Young's modulus and Poisson's ratio of the hollow cylinder of the elastic material, the inherent mass and wire diameter of the optical fiber itself, and the length, number of turns, diameter, height, etc. of the optical fiber winding are closely related to the technical indicators such as sensitivity, frequency characteristics, linearity, distortion, and dynamic range of the tension-compression optical fiber detector. Some of them are also mutually restricted and must be comprehensively coordinated to achieve the best. For example: when the optical fiber is bent with a certain radius of curvature, radiation loss will occur. When the optical fiber is slightly bent and the radius of curvature is large, the radiation loss is very small, but the volume and weight also increase accordingly; when the radius of curvature decreases, the loss increases with the decrease in the radius of curvature. When the radius of curvature is small to a certain extent, the loss increases exponentially, so it must be comprehensively considered according to actual use needs.

[0067] The working principle and use process of the present invention:

[0068] After the present invention is installed, when the device is affected by external vibration, the mass block 2 vibrates with the external vibration, and the vibration acts on the spring sheet 3, so the spring sheet 3 also vibrates with the external vibration, and the vibration of the spring sheet 3 acts on the optical fiber winding 6 through the elastic hollow cylinder 4. In other words, since the vibration detected by the mass block 2 acts on the optical fiber winding 6, it causes axial deformation of the optical fiber winding 6, and the axial deformation causes radial deformation, so that the refractive index and length of the optical fiber change, so the measured light moves, while the reference light is fixed, forming a situation where one moves and the other is fixed, resulting in a change in the phase shift of the measured light, that is, the optical phase shift of the reference light changes, and the two interfere with each other. Then, using the interference measurement technology, the change in the optical phase shift is converted into a change in light intensity, and then through optical / electrical conversion and A / D conversion, the measured seismic wave signal can be measured.

[0069] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A PM-level tensile-compression high-sensitivity optical fiber detector, characterized in that: It comprises a mass block (2) and two winding mechanisms; The upper surface and the lower surface of the mass block (2) are both fixedly connected with spring sheets (3), and the two winding mechanisms are respectively arranged at the other ends of the two spring sheets (3); The structures of the two winding mechanisms are the same, wherein one of the winding mechanisms comprises an elastic hollow cylinder (4) fixedly connected to the upper surface of a spring sheet (3), a cylindrical bracket (5) having an outer diameter matching its inner diameter is fixedly connected to the interior of the elastic hollow cylinder (4), and an optical fiber winding (6) is wound around the outer surface of the elastic hollow cylinder (4).

2. A PM-level tensile-compression high-sensitivity optical fiber detector as claimed in claim 1, characterized in that: The mass block (2) and the two spring sheets (3) both have circular cross-sections.

3. The PM-level tensile-compression high-sensitivity optical fiber detector according to claim 1, characterized in that: The central axes of the mass block (2), the two spring sheets (3), the two elastic hollow cylinders (4), and the two cylindrical supports (5) are all located on the same straight line.

4. The PM-level tensile-compression high-sensitivity optical fiber detector according to claim 1, characterized in that: The cylindrical support (5) is made of metal.

5. The PM-level tensile-compression high-sensitivity optical fiber detector according to claim 1, characterized in that: The length of the cylindrical support (5) is shorter than the length of the elastic hollow cylinder (4), and the outer end surface of the cylindrical support (5) and the outer end surface of the elastic hollow cylinder (4) are located in the same plane.

6. The PM-level tensile-compression high-sensitivity optical fiber detector according to claim 1, characterized in that: The outer surfaces of the mass block (2) and the two winding mechanisms are sheathed with an outer shell (1) that matches the outer contour of the structure formed by combining the three.

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