Deformation sensing composite optical cable based on ultra-weak fiber grating

Abstract

The deformation sensing composite optical cable based on the ultra-weak fiber bragg grating comprises a multi-fiber surrounding layer and a protective layer, the multi-fiber surrounding layer is formed by surrounding a main supporting shaft by a plurality of optical fibers with the same diameter, and the plurality of optical fibers are ultra-weak grating optical fibers inscribed with ultra-weak fiber gratings and are used for deformation sensing; the other optical fiber is a common optical fiber; the protection layer wraps the multi-fiber surrounding layer, so that the multi-fiber surrounding layer is tightly attached to the main supporting shaft, and the optical cable is protected. The ultra-weak grating optical fiber adopts an encircling structure that an ultra-weak grating (uwFBG) optical fiber and a common optical fiber with the same diameter are wound around the main supporting shaft. The composite optical cable is simple in structure, the main supporting shaft can enable the sensing optical fiber not to generate self-torsion easily, and the problem that section shape sensing points are parallel can be solved; the ultra-weak grating fiber with ultra-high multiplexing degree can solve the problem of deformation sensing distance limitation, and is suitable for deformation detection of a large-scale structure.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, specifically to a deformation-sensing composite optical cable based on an ultra-weak fiber grating. Background Technology

[0002] Continuous and accurate deformation measurement of large structures such as pipelines, cables, bridges, and tunnels is a core technological means to ensure facility safety and achieve sustainable development. Continuous / long-term deformation monitoring data can form a "health record" for the structure, providing scientific assessment data for the design, use, operation, and maintenance of large structures.

[0003] Fiber optic deformation sensing technology has become a hot research topic in deformation measurement due to its distributed nature and inherent insulation. Multi-core optical fibers, with their multiple cores maintaining a parallel distribution, are the primary sensing method for fiber optic deformation sensing. However, their manufacturing process is complex and costly, and their length is limited to only 2-3 meters. This restricts their application to small-scale morphological measurements such as minimally invasive interventional navigation and modeling, and robot posture monitoring, and cannot meet the needs of large-scale structural deformation measurement.

[0004] Chinese patent "A Fiber Bragg Grating Shape Sensing Sensor" (application number: 202010365062.8) discloses a fiber Bragg grating shape sensing sensor and describes the structure of the shape-sensing optical cable in detail, but the manufacturing process is complex and difficult to implement. Chinese patent "A Marine Optoelectronic Composite Cable with Shape Sensing" (application number: 202410182481.6) discloses a marine optoelectronic composite cable with shape sensing; Chinese patent "A Three-Dimensional Shape Reconstruction System and Sensor Preparation Method Combining Grating Inversion Technology" (application number: 202411684300.6) discloses a method for preparing a three-dimensional shape sensor. Both patents solve the problem of combining shape-sensing optical cables with cable fabrication, but do not provide a detailed description of the shape-sensing optical cable itself. Harbin Engineering University (10.1109 / JSEN.2024.3429296) used an optical cable made of three Bragg grating (FBG) fibers to monitor the deformation of a 30m static submarine cable. To ensure the parallelism of the three fibers, the calibration method limited the cable's fabrication length.

[0005] Therefore, there is currently no deformation sensing optical cable that can meet the needs of long-distance deformation monitoring. Summary of the Invention

[0006] This invention provides a deformation sensing composite optical cable based on an ultra-weak fiber grating. The composite optical cable has a simple structure, and the main support shaft can prevent the sensing fiber from self-twisting, thus solving the problem of parallelism of the sensing points for cross-sectional shape. Combined with ultra-weak fiber grating with ultra-high multiplexing, it can solve the limitation of deformation sensing distance and is suitable for deformation detection of large structures.

[0007] The technical solution adopted in this invention is as follows: A deformation-sensing composite optical cable based on ultra-weak fiber Bragg gratings, the composite optical cable includes: a multi-fiber wrapping layer and a protective layer; The multi-fiber surrounding layer is composed of multiple optical fibers of the same diameter surrounding the main support axis. Among them, multiple optical fibers are ultra-weak fiber grating fibers with inscriptions of ultra-weak fiber gratings, which are used for deformation sensing; the other optical fibers are ordinary optical fibers. The protective layer covers the multi-fiber wrapping layer, ensuring a tight fit between the multi-fiber wrapping layer and the main support shaft, and protecting the optical cable.

[0008] The ultra-weak grating fiber is an optical fiber with an ultra-weak grating (uwFBG) written on it, and a structure in which ordinary optical fibers of the same diameter are wrapped around the main support axis.

[0009] The main support shaft is surrounded by 12 optical fibers of the same diameter: 3 ultra-weak grating fibers and 9 ordinary fibers, forming a "1+12" surround structure. The surround structure places the 3 ultra-weak grating fibers on the same circumference, with the included angle between any two ultra-weak grating fibers being 120°.

[0010] The diameter D of the main support shaft and the diameter d of the optical fiber should satisfy the following relationship: .

[0011] The protective layer is equipped with marking lines to track the rotation of the optical cable itself.

[0012] The protective layer is made of polyolefin-coated multi-fiber wrapping layer, and a marking line is sprayed on the outer surface along the cable-forming direction to follow one of the ultra-weak grating optical fibers to track the rotation of the optical cable itself.

[0013] The main support shaft is made of titanium-nickel shape memory alloy, which has a shape memory effect and is used for positioning the central axis of the optical cable and for deformation recovery.

[0014] The submarine cable deformation measurement system consists of a deformation-sensing composite optical cable inserted into the central gap of the submarine cable under test, and the portion of the deformation-sensing composite optical cable not inserted into the submarine cable fixed on the optical cable fixing base. The ultra-weak grating optical fiber is connected to the ultra-weak grating demodulation module, and the ultra-weak grating demodulation module is connected to the host computer.

[0015] The method for measuring submarine cable deformation includes the following steps: S1: Insert the deformation sensing composite optical cable into the central gap of the submarine cable to be tested. The gap extends along the center of the submarine cable, and the deformation sensing composite optical cable located in it is basically located on the center line of the submarine cable. S2: Fix the part of the deformation sensing composite optical cable that is not inserted into the submarine cable to the optical cable fixing seat, and connect the three ultra-weak grating optical fibers in the optical cable to the three wavelength demodulation channels of the ultra-weak grating demodulation module. S3: Straighten the submarine cable under test, and the host computer records all the grating wavelengths in the three ultra-weak grating optical fibers transmitted by the ultra-weak grating demodulation module. The wavelengths of the three ultra-weak fiber gratings on the same cross section of the deformation sensing composite optical cable are a set of wavelength information, called the initial wavelength. S4: When the submarine cable under test undergoes deformation and bending, the wavelengths of the three ultra-weak fiber gratings 7 on the same cross section of the deformation sensing composite optical cable are transmitted to the host computer again by the ultra-weak grating demodulation module and recorded as the deformation wavelength. S5: In the host computer, the strain at the location of the grating point is first calculated based on the initial wavelength and the deformation wavelength. Then, the bending information of the center point of the submarine cable at the cross section is obtained according to the distribution of the grating points on the cross section, that is, the curvature and bending direction of the submarine cable under test at this point. The bending direction at this point is corrected according to the marking line trajectory on the deformation sensing composite optical cable. Finally, the bending data at each point are connected by integration to obtain the deformation curve, which enables the sensing of submarine cable deformation.

[0016] This invention discloses a deformation-sensing composite optical cable based on an ultra-weak fiber Bragg grating, with the following technical advantages: 1) The deformation-sensing composite optical cable proposed in this invention uses uwFBG as the sensing unit. Its weakly reflected light has a higher power than the backscattered and reflected light of ordinary optical fibers, providing a sensing signal with a higher signal-to-noise ratio. Furthermore, its low reflectivity allows for the etching of a large number of gratings within the same fiber, with no constraint on the grating spacing and sensing length, thus overcoming the distance limitations of ordinary optical fiber demodulation methods. Using uwFBG as the sensing unit overcomes the problem of mutual constraints between sensing spatial resolution and sensing distance. The titanium-nickel alloy ensures the optical cable is twist-free and has high recoverability. The manufacturing cost of the composite optical cable is far lower than that of multi-core optical fibers, enabling its application in long-distance, large-scale structure shape monitoring.

[0017] 2) The deformation-sensing composite optical cable proposed in this invention uses a titanium-nickel alloy as the main support shaft. The memory effect of the alloy ensures that the optical cable can return to its parallel state during manufacturing after assembly and transportation. The high elasticity of the titanium-nickel alloy also enables the optical cable to have good recovery after deformation caused by the tested object. Using the titanium-nickel alloy as the main support shaft solves the problem of consistency in the state of optical cable during coiling, transportation, deployment, and deformation.

[0018] 3) The deformation-sensing composite optical cable proposed in this invention adopts a "1+12" loop structure. Through appropriate main shaft and outer bundle diameters, the three sensing optical fibers can be naturally maintained on the same circumference and at a 120° angle to meet the sensing position requirements. Compared with the "1+6" equal-diameter cable, the ratio of a large main shaft diameter to a small outer bundle diameter ensures that the three sensing optical fibers will not misalign or twist when compressed by the outer protective layer, thus guaranteeing the parallel arrangement of the sensing optical fibers. Attached Figure Description

[0019] The present invention will be further described below with reference to the accompanying drawings and examples; Figure 1 This is a three-dimensional structural diagram of a deformation-sensing composite optical cable based on an ultra-weak fiber grating. Figure 2 This is a schematic diagram of the axial cross-section of the deformation-sensing composite optical cable. Figure 3 A schematic diagram of the cross-sectional structure of a deformation-sensing composite optical cable embedded in a submarine cable. Figure 4 This is a schematic diagram of the structure of a submarine cable deformation measurement system.

[0020] Among them: 1-deformation sensing composite optical cable, 2-main support shaft, 3-ultra-weak grating optical fiber, 4-ordinary optical fiber, 5-protective layer, 6-marking line, 7-ultra-weak fiber grating, 8-submarine cable under test, 9-ultra-weak grating demodulation module, 10-host computer, 11-optical cable fixing base and optical fiber connection device. Detailed Implementation

[0021] A deformation-sensing composite optical cable based on an ultra-weak fiber Bragg grating, the composite optical cable having a circular cross-section, comprising: Multi-fiber surrounding layer, protective layer 5; The multi-fiber surrounding layer is composed of multiple optical fibers of the same diameter surrounding the main support axis 2. Among them, the multiple optical fibers are ultra-weak grating optical fibers 3 with ultra-weak fiber gratings 7 inscribed on them, which are used for deformation sensing; the other optical fibers are ordinary optical fibers 4. The protective layer 5 is hot-extruded from a composite material with medium Young's modulus and good resilience. The protective layer 5 covers the multi-fiber wrapping layer, ensuring a tight fit between the multi-fiber wrapping layer and the main support shaft 2, and protecting the optical cable; The ultra-weak grating fiber 3 is an optical fiber with an ultra-weak grating (uwFBG) with a spacing. The ultra-low reflectivity of the ultra-weak grating (uwFBG) allows tens of thousands of sensors to be deployed on a single grating. Its reflected signal has a higher signal-to-noise ratio than the intrinsic reflected light of ordinary optical fiber 4, which can solve the problems of weak sensing signal and mutual limitation of spatial resolution and detection distance of ordinary optical fiber.

[0022] A structure in which ordinary optical fibers of the same diameter 4 are wound around the main support shaft 2.

[0023] The main support shaft 2 is surrounded by 12 optical fibers of the same diameter: 3 ultra-weak grating fibers 3 and 9 ordinary optical fibers 4, forming a "1+12" surrounding structure. The surrounding structure places the 3 ultra-weak grating fibers 3 on the same circumference, with the included angle between any two ultra-weak grating fibers 3 being 120°.

[0024] The diameter D of the main support shaft 2 and the diameter d of the optical fiber should satisfy the following relationship: .

[0025] The protective layer 5 is provided with marking lines 6 for tracking the rotation of the optical cable itself.

[0026] The protective layer 5 is made of polyolefin-coated multi-fiber wrapping layer, and a marking line 6 is sprayed on the outer surface along the cable forming direction to follow one of the ultra-weak grating optical fibers 3 to track the rotation of the optical cable itself.

[0027] The outermost layer is the protective layer 5, which is made of composite material polyolefin hot extrusion molding, so that the twelve optical fibers tightly surround the main support shaft 2, which plays the role of protecting the ultra-weak grating optical fiber 3.

[0028] The main support shaft 2 is made of titanium-nickel shape memory alloy, which has a shape memory effect and is used for positioning the central axis of the optical cable and for deformation recovery. It has strong resistance to tensile deformation. The main support shaft 2 is made of titanium-nickel shape memory alloy wire, whose shape memory effect can ensure the original straight state of the entire sensing optical cable, and its superelasticity allows the optical cable to return to its original shape after deformation.

[0029] The materials and structure used in the deformation sensing composite optical cable 1 can reduce the self-torsion of the optical cable during production and transportation, while ensuring the relative position requirements between sensing fibers, reducing the measurement error caused by the non-uniformity of the optical cable, and improving the accuracy of optical cable shape sensing.

[0030] Example 1: Realization of ultra-weak grating fiber deformation sensing optical cable: (1) First, ultra-weak grating fiber 3 is made by writing ultra-weak gratings with a spacing of 0.2 meters on ordinary optical fiber 4 with a diameter of d of 0.9 mm using ultraviolet light, and then marking the outer surface of each fiber grating point.

[0031] (2) According to the calculation formula The diameter of the main support shaft was calculated to be less than 2.6 mm, and a titanium-nickel alloy wire with a diameter of 2.5 mm was selected as the main support shaft 2.

[0032] (3) With the titanium-nickel alloy wire as the center, twelve 0.9mm optical fibers are placed in parallel around it. The arrangement is repeated in the order of one ultra-weak grating fiber 3 and two ordinary optical fibers 4 until it surrounds the titanium-nickel alloy wire, while ensuring that the grating mark on each ultra-weak grating fiber 3 is aligned.

[0033] (4) The protective layer 5 is made of polyolefin material and is extruded through a circular mold to cover the cable with a “1+12” structure. The coating thickness is 0.6mm. At the same time, a marking line 6 is sprayed on the outer surface along the cable-making direction, following one of the ultra-weak grating optical fibers 3, and finally a deformation sensing composite optical cable 1 with a diameter of 5.5mm is synthesized.

[0034] Example 2: Application of Deformation Sensing Composite Optical Cable 1 in Submarine Cable Deformation Measurement, Taking Zhongtian Three-Core Cable as an Example: (1) Insert the deformation sensing composite optical cable 1 in Example 1 into the central gap of the submarine cable 8 to be tested. The gap extends along the center of the submarine cable, and the deformation sensing composite optical cable 1 located therein is basically located at the center line of the submarine cable. The gap space can accommodate a round cable with a diameter of about 8 mm, which is slightly larger than the diameter of the deformation sensing composite optical cable 1, so as to ensure that the composite optical cable can deform accordingly when the submarine cable deforms without generating additional stress and strain. (2) Fix the part of the deformation sensing composite optical cable 1 that is not inserted into the submarine cable to the optical cable fixing seat, and connect the three ultra-weak grating optical fibers 3 in the optical cable to the three wavelength demodulation channels of the ultra-weak grating demodulation module 9. (3) Straighten the submarine cable 8 to be tested. The data processing software of the host computer 10 records all the grating wavelengths of the three ultra-weak grating optical fibers 3 transmitted by the ultra-weak grating demodulation module 9. The wavelengths of the three ultra-weak fiber gratings 7 on the same cross section of the deformation sensing composite optical cable 1 are a set of wavelength information, called the initial wavelength. (4) When the submarine cable 8 under test is deformed and bent, the wavelengths of the three ultra-weak fiber gratings 7 on the same cross section of the composite optical cable 1 are transmitted again to the data processing software of the host computer 10 by the ultra-weak grating demodulation module 9 and recorded as the deformation wavelength. (5) In the data processing software of the host computer 10, the strain at the location of the grating point is first calculated based on the initial wavelength and the deformation wavelength. Then, the bending information of the corresponding center point of the submarine cable at the cross section is obtained according to the distribution of the grating points on the cross section, that is, the curvature and bending direction of the submarine cable 8 under test at this location. The bending direction at this location is then corrected according to the trajectory of the marking line 6 on the composite optical cable. Finally, the bending data of each point are connected by the integration method to obtain the deformation curve, thus realizing the sensing of the deformation of the submarine cable.

Claims

1. A deformation-sensing composite optical cable based on ultra-weak fiber Bragg gratings, characterized in that: The composite optical cable includes: Multifiber surrounding layer, protective layer (5); The multi-fiber surrounding layer is composed of multiple optical fibers of the same diameter surrounding the main support axis (2), among which multiple optical fibers are ultra-weak grating fibers (3) with ultra-weak fiber gratings (7) written on them, used for deformation sensing; the other optical fibers are ordinary optical fibers (4). The protective layer (5) covers the multi-fiber wrapping layer, so that the multi-fiber wrapping layer fits tightly with the main support shaft (2) and protects the optical cable.

2. The deformation-sensing composite optical cable based on ultra-weak fiber Bragg grating according to claim 1, characterized in that: The ultra-weak grating fiber (3) is an optical fiber with an ultra-weak grating (uwFBG) written on it, and a common optical fiber (4) of the same diameter is wrapped around the main support axis (2).

3. The deformation-sensing composite optical cable based on an ultra-weak fiber Bragg grating according to claim 2, characterized in that: The main support shaft (2) is surrounded by 12 optical fibers of the same diameter: 3 ultra-weak grating optical fibers (3) and 9 ordinary optical fibers (4), forming a "1+12" surrounding structure; the surrounding structure places the 3 ultra-weak grating optical fibers (3) on the same circumference, and the included angle between any two ultra-weak grating optical fibers (3) is 120°.

4. The deformation-sensing composite optical cable based on an ultra-weak fiber Bragg grating according to claim 3, characterized in that: The diameter D of the main support shaft (2) and the diameter d of the optical fiber satisfy the following relationship: 。 5. The deformation-sensing composite optical cable based on an ultra-weak fiber Bragg grating according to claim 4, characterized in that: The protective layer (5) is provided with marking lines (6) for tracking the rotation of the optical cable itself.

6. The deformation-sensing composite optical cable based on an ultra-weak fiber grating according to claim 5, characterized in that: The protective layer (5) is made of polyolefin-coated multifiber wrapping layer, and a marking line (6) is sprayed on the outer surface along the cable-forming direction to follow one of the ultra-weak grating optical fibers (3) to track the rotation of the optical cable itself.

7. The deformation-sensing composite optical cable based on an ultra-weak fiber Bragg grating according to claim 6, characterized in that: The main support shaft (2) is made of titanium-nickel shape memory alloy, which has a shape memory effect and is used for positioning the central axis of the optical cable and for deformation recovery.

8. A submarine cable deformation measurement system using a deformation-sensing composite optical cable as described in any one of claims 1 to 7, characterized in that... include: The deformation sensing composite optical cable (1) is inserted into the central gap of the submarine cable (8) to be tested. The part of the deformation sensing composite optical cable (1) that is not inserted into the submarine cable is fixed on the optical cable fixing seat. The ultra-weak grating fiber (3) is connected to the ultra-weak grating demodulation module (9). The ultra-weak grating demodulation module (9) is connected to the host computer (10).

9. The method for preparing a deformation-sensing composite optical cable as described in any one of claims 1 to 7, characterized in that: 1) First, ultra-weak grating fiber (3) is made by writing ultra-weak gratings on ordinary optical fiber (4) with ultraviolet light, and then marking the outer surface of each fiber grating point position; 2) According to the calculation formula Calculate the diameter of the main support shaft and select titanium-nickel alloy wire as the main support shaft (2). 3) With the titanium-nickel alloy wire as the center, twelve optical fibers are placed in parallel around it. The arrangement is repeated in the order of one ultra-weak grating fiber (3) and two ordinary optical fibers (4) until it surrounds the titanium-nickel alloy wire, while ensuring that the grating mark on each ultra-weak grating fiber (3) is aligned. 4) The protective layer (5) is made of polyolefin material and is extruded and wrapped around the cable through a circular mold. At the same time, a marking line (6) is sprayed on the outer surface along the cable-forming direction following one of the ultra-weak grating optical fibers (3), and finally the deformation sensing composite optical cable (1) is synthesized.

10. A method for measuring the deformation of a submarine cable using a deformation-sensing composite optical cable as described in any one of claims 1 to 7, characterized in that... Includes the following steps: S1: Insert the deformation sensing composite optical cable (1) into the central gap of the submarine cable (8) to be tested. The gap extends along the center of the submarine cable, and the deformation sensing composite optical cable (1) located therein is basically located at the center line of the submarine cable. S2: Fix the part of the deformation sensing composite optical cable (1) that is not inserted into the submarine cable to the optical cable fixing seat, and connect the three ultra-weak grating optical fibers (3) in the optical cable to the three wavelength demodulation channels of the ultra-weak grating demodulation module (9). S3: Straighten the submarine cable (8) to be tested, and the host computer (10) records all the grating wavelengths in the three ultra-weak grating optical fibers (3) transmitted by the ultra-weak grating demodulation module (9). The wavelengths of the three ultra-weak fiber gratings (7) on the same cross section of the deformation sensing composite optical cable (1) are a set of wavelength information, called the initial wavelength. S4: When the submarine cable under test (8) is deformed and bent, the wavelengths of the three ultra-weak fiber gratings (7) on the same cross section of the deformation sensing composite optical cable (1) are transmitted to the host computer (10) again by the ultra-weak grating demodulation module (9), and recorded as the deformation wavelength. S5: In the host computer (10), the strain at the location of the grating point is first calculated based on the initial wavelength and the deformation wavelength. Then, the bending information of the corresponding center point of the submarine cable at the cross section is obtained according to the distribution of the grating points in the cross section, that is, the curvature and bending direction of the submarine cable (8) under test at this point. The bending direction at this point is corrected according to the trajectory of the marking line (6) on the deformation sensing composite optical cable (1). Finally, the bending data at each point are connected by the integral method to obtain the deformation curve, which enables the sensing of submarine cable deformation.

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