Optical fiber bending sensor capable of sensing different bending directions as well as preparation method and test method of optical fiber bending sensor

Abstract

The invention provides an optical fiber bending sensor capable of sensing different bending directions and a preparation method and a testing method thereof, and belongs to the technical field of sensors. The optical fiber bending sensor comprises a polyimide optical fiber and a silica gel protection layer wrapping the outer side of the polyimide optical fiber; a graphene layer is arranged on the cladding of the polyimide optical fiber; the graphene layer comprises a plurality of non-contact graphene conductive short wires arranged on the polyimide optical fiber cladding, and the graphene conductive short wires are parallel to the optical axis of the polyimide optical fiber; the plurality of graphene conductive short wires are asymmetrically arranged on the cross section of the polyimide optical fiber, and the graphene conductive short wires are different in size and electrical property; a silver deposition layer is attached to the graphene layer; the two ends of the graphene conductive short wire are coated with conductive silver adhesive electrodes. According to the invention, bending sensing in multiple directions can be realized, the preparation cost is low, the preparation process is simple, and the preparation efficiency is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of sensors, and in particular is an optical fiber bending sensor capable of sensing different bending directions and a preparation method and a testing method thereof. Background Art

[0002] As an advanced sensing device based on optical fiber technology, optical fiber bend sensor is widely used in structural health monitoring, traffic monitoring and environmental monitoring. Its basic principle is to monitor the bending by detecting the changes in optical properties (such as changes in light intensity, phase or wavelength) caused by force or bending of the optical fiber. However, traditional optical fiber bend sensors can usually only sense the bending angle in a specific direction, which limits its application in complex and changing environments. Especially in dynamic environments with multi-directional deformation and multiple forces, the sensor cannot fully and accurately reflect the true state of the structure. Therefore, the development of a bend sensor that can overcome the limitation of single-direction sensing is of great significance to improving its application effect in complex environments. Summary of the invention

[0003] The present invention provides an optical fiber bending sensor capable of sensing different bending directions and a preparation method and a testing method thereof, aiming to solve the problem that traditional optical fiber bending sensors can only sense a single direction. The present invention realizes effective monitoring of bending in multiple directions by making innovative designs on optical fibers. It is worth noting that the bending sensor of the present invention realizes accurate perception of bending in multiple directions without affecting the original optical properties of the optical fiber, providing a new solution for structural health monitoring in complex environments.

[0004] Technical solution: The present invention discloses a multifunctional optical fiber capable of sensing different bending directions, comprising a polyimide optical fiber and a silicone protective layer coated on the outside of the polyimide optical fiber; a graphene layer is provided on the cladding of the polyimide optical fiber; the graphene layer comprises a plurality of non-contacting graphene conductive short wires arranged on the polyimide optical fiber cladding, and the graphene conductive short wires are parallel to the optical axis of the polyimide optical fiber; the plurality of graphene conductive short wires are asymmetrically arranged on the cross section of the polyimide optical fiber, and the sizes and electrical properties of the graphene conductive short wires are different; a silver deposition layer is attached to the graphene layer; and conductive silver glue electrodes are coated on both ends of the graphene conductive short wires.

[0005] Furthermore, the size refers to the length and width of the graphene conductive short wire, and the electrical property refers to the resistance value and electromagnetic radiation property of the graphene conductive short wire.

[0006] Furthermore, there are at least two graphene conductive short wires.

[0007] Furthermore, the silicone protective layer is a PDMS protective layer.

[0008] The present invention discloses a method for preparing the above-mentioned multifunctional optical fiber capable of sensing different bending directions, comprising the following steps:

[0009] Step 1: Inducing the generation of multiple non-contacting graphene conductive short wires with different sizes and different electrical properties at different positions of the polyimide optical fiber cladding parallel to the optical axis by laser; the multiple graphene conductive short wires are asymmetrically arranged on the cross section of the polyimide optical fiber.

[0010] Step 2: using electroplating to attach a layer of metallic silver to the surface of the graphene layer;

[0011] Step 3: Use conductive silver glue to coat both ends of the graphene conductive short wire as electrodes, and use a vacuum drying oven to evacuate and air-dry the conductive silver glue electrodes;

[0012] Step 4: Encapsulate a silicone protective layer on the outside of the polyimide optical fiber.

[0013] Furthermore, in step 1, the laser induced generation method is:

[0014] The polyimide fiber cladding is used as a carrier for preparing laser-induced graphene. A CO2 laser is used to induce high temperature to generate laser-induced graphene at the polyimide fiber cladding position along the optical axis of the fiber. After a short graphene conductive line is generated, the angle of the polyimide fiber is rotated along the optical axis of the fiber, the laser scanning parameters are adjusted, and the CO2 laser is used again to induce high temperature to generate the next short graphene conductive line. This method is performed multiple times to eventually form a graphene layer containing multiple short graphene conductive lines.

[0015] Furthermore, in the laser induced generation method, the laser scanning parameters are: the wavelength of the CO2 laser is 10.6 μm, the laser spot diameter at the focus is 50 μm, the laser power is adjustable within 0.01-30 W, and the laser scanning speed is adjustable within 1-1000 mm / s.

[0016] Further, in step 2, the electroplating method is specifically:

[0017] The graphene conductive short wire is electroplated by an electrochemical deposition method, a silver metal layer is deposited on the graphene conductive short wire, and the thickness of the silver metal layer is adjusted by adjusting the electroplating parameters;

[0018] The electroplating parameters include current size and electroplating time; the current size is controlled to be 0.001A-0.004A, the electroplating time is 10-30 minutes, and the thickness of the generated silver metal layer is 20-40μm.

[0019] Furthermore, in step three, the temperature of the vacuum drying oven is set to 60° C., and the heating time is 20 minutes.

[0020] Furthermore, in step 4, the thickness of the silicone protective layer is in the range of 20-80 μm.

[0021] Furthermore, the specific operation of step four is: coating the PDMS flexible material on the surface of the graphene optical fiber prepared in step three, and curing the PDMS material through a vacuum drying oven and a rotating motor device.

[0022] Furthermore, in step 4, before coating, the graphene clad optical fiber is subjected to plasma treatment and silanization treatment.

[0023] The invention also discloses a testing method of an optical fiber bending sensor capable of sensing different bending directions. The optical fiber bending sensor tests bending characteristics by a wired testing method or a wireless testing method.

[0024] Furthermore, the wired testing method uses a wire to lead out the conductive silver glue electrode, and uses a resistance measuring device to monitor the resistance values ​​at both ends of all graphene conductive short lines in the graphene layer in real time. When the graphene conductive short line bends outward, the resistance of the graphene conductive short line increases; when the graphene conductive short line bends inward, the resistance of the graphene conductive short line decreases. The bending angle is quantitatively analyzed based on the resistance change rate to achieve the measurement of multi-directional bending deformation.

[0025] Furthermore, the wireless testing method is as follows: the conductive silver glue electrode is led out by connecting a coaxial feeder, a graphene conductive short wire is used as an antenna, an antenna signal is sent from the graphene conductive short wire to the outside world, a highly sensitive signal receiving device is used to capture the electromagnetic wave signal emitted from the antenna, and the bending degree of the antenna is indirectly measured by analyzing the change in signal strength; under different bending degrees, the electromagnetic radiation characteristics brought by the graphene conductive short wire also change accordingly, thereby increasing or decreasing the signal transmission efficiency, and the signal strength at the receiving end is correspondingly enhanced or weakened.

[0026] Beneficial effects of the present invention:

[0027] 1) The present invention can realize bending sensing in multiple directions, and at the same time has low preparation cost, simple preparation process and high preparation efficiency.

[0028] 2) The present invention uses laser-induced graphene technology to make the sensing part of the bending sensor, and can prepare the graphene sensing unit without a mask, and uses PDMS flexible material for curing and packaging. The method has low cost, simple preparation process and high preparation efficiency.

[0029] 3) The present invention reduces the resistance value by plating silver on the graphene conductive short wires, thereby enhancing the surface properties of the graphene layer under bending strain. The silver deposition layer can increase the conductivity and stability of the graphene.

[0030] 4) The present invention combines laser-induced graphene with optical fiber, utilizing the excellent electrical properties of the graphene layer and the arbitrary bending of the optical fiber, thereby overcoming the disadvantage that the optical fiber bending sensor can only sense bending in a single direction at a fixed angle, broadening the application scenarios of laser-induced graphene in optical fiber bending sensors, and having great application prospects in the fields of bending sensing and electrical signal transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a schematic diagram of the structure of the optical fiber bending sensor capable of sensing different bending directions in Example 1;

[0032] Among them, polyimide optical fiber-1, first graphene conductive short wire-2, second graphene conductive short wire-3, silver deposition layer-4, conductive silver glue electrode-5, silicone protective layer-6;

[0033] Figure 2 1 is a cross-sectional and side schematic diagram of the optical fiber bending sensor in Example 2 of the present invention; wherein a is a cross-sectional schematic diagram, and b is a side schematic diagram;

[0034] Figure 3 is a schematic diagram illustrating multi-directional bending of the optical fiber bending sensor in Example 3;

[0035] Figure 4 is a schematic diagram of using the resistance values ​​of two graphene conductive short lines of the optical fiber bending sensor in Example 3 to distinguish directions;

[0036] Figure 5 is a schematic diagram of the resistance change rate in the direction when the optical fiber bending sensor in Example 3 is bent on one side; DETAILED DESCRIPTION

[0037] The technical solution of the present invention is described in detail below through embodiments, but the protection scope of the present invention is not limited to the embodiments.

[0038] Embodiment 1: Optical fiber bending sensor capable of sensing different bending directions

[0039] like Figure 1As shown, the optical fiber bending sensor prepared in this embodiment includes a polyimide optical fiber 1 and a silicone protective layer 6 coated on the outside of the polyimide optical fiber. A graphene layer is provided on the cladding of the polyimide optical fiber 1, and the graphene layer includes two non-contacting graphene conductive short wires arranged on the cladding of the polyimide optical fiber 1, and the two graphene conductive short wires are parallel to the optical axis of the polyimide optical fiber; the two graphene conductive short wires are asymmetrically arranged on the cross section of the polyimide optical fiber 1, and the size and electrical characteristics of the graphene conductive short wires are different; the different size refers to the different length and width of the graphene conductive short wires, and the different electrical characteristics refer to the different resistance value and electromagnetic radiation characteristics of the graphene conductive short wires; the two graphene conductive short wires are respectively a first graphene conductive short wire 2 and a second graphene conductive short wire 3. A silver deposition layer 4 is attached to the graphene layer; and conductive silver glue electrodes 5 are coated on both ends of the graphene conductive short wires.

[0040] Example 2: Preparation of the optical fiber bending sensor for sensing different bending directions in Example 1

[0041] The preparation method is as follows:

[0042] Step 1: Inducing the generation of two non-contacting graphene short conductive lines with different sizes and different electrical properties at different positions of the polyimide optical fiber cladding parallel to the optical axis by laser; the plurality of graphene short conductive lines are asymmetrically arranged on the cross section of the polyimide optical fiber.

[0043] In this embodiment, the specific steps of step one are as follows:

[0044] 1) In this embodiment, polyimide optical fiber is selected as the substrate of the laser-induced graphene sensor. The diameter of the polyimide optical fiber is 180 microns, and the thickness of the polyimide layer is 55 microns. A straight line pattern for forming a graphene conductive short line is drawn by the laser control software of the host computer;

[0045] 2) Place the optical fiber under the red light indicator line of the CO2 laser and align the optical fiber with the red light indicator line. Control the upper computer software to use the CO2 laser to induce high temperature to generate a graphene layer on the polyimide optical fiber cladding (polyimide film). The specific operation is: use the CO2 laser to generate a graphene conductive short line along the optical axis, and then rotate it 90° along the optical axis. The purpose is to form an asymmetric structure of graphene conductive short lines on the 360° cladding of the optical fiber. At the same time, change the CO2 laser parameters to distinguish the bends in different directions, and prepare a graphene conductive short line on the optical fiber cladding again.

[0046] Each graphene conductive short line is parallel to the optical axis, and the electrical characteristic resistance value of each graphene conductive short line is different due to different laser scanning parameters, so as to distinguish the resistance bending changes in different directions.

[0047] In this embodiment, the length of the first graphene conductive short line 2 is 3 cm, and the short line width is 110 μm; the length of the second graphene conductive short line 3 is 2.5 cm, and the short line width is 125 μm.

[0048] The quality of the generated laser-induced graphene can be controlled by adjusting the laser power and the laser scanning speed. The laser marking position is accurately positioned on the optical fiber cladding and the two laser-marked graphene layers are non-contacting. Due to the different laser scanning parameters, the electrical properties of the two graphene conductive short lines are different. The first graphene conductive short line is longer, the scanning power is low, and the carbonization degree is low. Therefore, the first graphene conductive short line has a larger resistance value than the second conductive short line. Figure 4 As shown, this is used to distinguish sensing in different directions. At the same time, the preparation of graphene conductive short wires at 0° and 90° ensures the asymmetry of the structure.

[0049] The graphene layer adjusts the CO2 laser high temperature induced position by rotating the optical fiber along the optical axis, and changes the CO2 laser high temperature induced parameters (laser scanning speed, laser scanning power, etc.) to generate two graphene conductive short lines at different positions, and the electrical characteristics of each graphene conductive short line are different. The polyimide optical fiber cladding is used as a carrier for growing laser-induced graphene, combining the conductive properties of graphene with the arbitrary angle bendability of the optical fiber. In this embodiment, a CO2 laser is used to induce high temperature at different positions of the polyimide optical fiber cladding parallel to the optical axis to generate two laser-induced graphene conductive short lines. Each graphene conductive short line has different sizes and electrical characteristics according to its different laser induced parameters (laser scanning speed, laser power), and ensures that the graphene is an asymmetric structure on the optical fiber cladding.

[0050] Step 2: Use electroplating to attach a layer of metallic silver to the surface of the graphene layer.

[0051] The graphene conductive short wires on the optical fiber cladding are electroplated by electrochemical deposition, and a silver metal layer is deposited on the graphene conductive short wires. The thickness of the silver metal layer is adjusted by adjusting the electroplating parameters, such as the current and the electroplating time, thereby enhancing the stability of the graphene layer under mechanical bending strain and enhancing the conductivity of the graphene layer.

[0052] In this embodiment, when the two graphene conductive short wires are electroplated with silver, the current is set to 0.0015A, the electroplating time is 20 minutes, and the thickness of the silver layer is 30μm. The two graphene conductive short wires are subjected to electroplating experiments respectively, and the electroplating parameters are the same. Due to the different resistances of the graphene conductive short wires themselves, the density of the silver particles in the corresponding electroplated silver layer is different, and the thickness of the silver layer is about 20-40μm.

[0053] The specific operations of step 2 are:

[0054] The graphene conductive short wire sample was electroplated using an electrochemical workstation to improve its stability and reduce the resistance value of the graphene conductive short wire. A three-electrode system was used, including a working electrode, a counter electrode and a reference electrode. The working electrode fixed the graphene conductive short wire sample to be electroplated, the counter electrode was a silver electrode, and the reference electrode was a silver chloride electrode.

[0055] Place the plating solution in a constant temperature water bath at a set temperature. Place the graphene conductive short wire working electrode in the plating solution to ensure that a constant current state is maintained between the cathode and the anode. Set the current size and electroplating time through the electrochemical workstation to control the thickness of the silver deposition layer. After the electroplating is completed, take out the electroplated graphene conductive short wire sample and thoroughly wash it with deionized water to remove the residual plating solution. Subsequently, place the sample in a drying oven for drying, and finally complete the electroplating step. Through the above steps, a silver layer can be successfully deposited on the surface of the graphene conductive short wire, improving the electrical properties of the graphene layer and enhancing the surface performance.

[0056] The plating solution is prepared using a thiosulfate cyanide-free silver plating system. The specific plating solution preparation process is as follows: the raw materials used are ionized water, which is used to dissolve sodium thiosulfate (with a concentration of 250g / L), potassium pyrosulfite (with a concentration of 45g / L) and silver nitrate (with a concentration of 45g / L). First, under stirring, the potassium pyrosulfite solution is added dropwise to the silver nitrate solution, and a turbid liquid with a white precipitate is formed. Then, sodium thiosulfate is added to this turbid liquid under stirring, and a slightly yellow and transparent solution can be obtained. Finally, a brightener and an anode activator are added to the solution to complete the preparation of the plating solution. Among them, the ratio of the brightener is nicotinic acid 4g / L and polyethyleneimine 0.08g / L, and the anode activator is thiosemicarbazide, with a concentration of 0.6g / L.

[0057] Step 3: Use conductive silver glue to coat both ends of the graphene conductive short wire as conductive silver glue electrodes, and use a vacuum drying oven to evacuate and air-dry the conductive silver glue electrodes. The conductive silver glue was purchased from Shenzhen Luxianzi Technology Co., Ltd. The temperature of the vacuum drying oven was set to 60°C and the heating time was 20 minutes.

[0058] Step 4: Finally, a silicone protective layer is encapsulated on the outside of the polyimide optical fiber.

[0059] The PDMS flexible material is evenly coated on the graphene optical fiber cladding by using the pulling method, and the PDMS material is cured by using a vacuum drying oven and a rotating motor device.

[0060] The silicone protective layer uses PDMS (polydimethylsiloxane material) flexible material. The silver-plated graphene optical fiber is immersed in the PDMS solution, and the PDMS flexible material is evenly coated on the optical fiber cladding using the pulling method. The PDMS material is cured using a vacuum drying oven and a rotating motor device. The graphene layer can be protected by coating with PDMS to prevent the graphene layer from falling off due to physical wear. The polyimide-coated optical fiber was purchased from Nanjing Jingcui Optical Technology Co., Ltd., and the PDMS material was purchased from Dow Corning, USA.

[0061] The specific operations of step 4 are:

[0062] 1) Using PDMS flexible polymer material to encapsulate graphene clad optical fiber, the ratio of PDMS substrate and curing agent is 10:1, and weighing is performed using a laboratory balance. After the ratio is determined, the PDMS solution is placed in a vacuum drying oven for vacuuming to remove bubbles in the prepared solution;

[0063] 2) In order to make the PDMS solution fit closely to the graphene material, the graphene-clad optical fiber is pretreated, including plasma treatment and silanization treatment. Plasma treatment can introduce oxygen-containing functional groups on the silver-plated graphene surface, increase its surface energy, and improve adhesion to PDMS; silanization treatment introduces silane groups on the silver-plated graphene surface to enhance its chemical bonding with PDMS. The pretreated graphene surface is more hydrophilic and has better adhesion to PDMS, which is beneficial to the subsequent encapsulation process.

[0064] 3) Slowly immerse the optical fiber into the vacuumed PDMS solution, and then pull the optical fiber out of the solution at a constant speed. The thickness of the coating can be controlled by controlling the pulling speed, the viscosity of the solution, and the immersion time of the optical fiber. Generally, a slower pulling speed will form a thicker coating, while a faster speed will form a thinner coating.

[0065] The pull-out speed ranges from 5 mm / min to 30 mm / min, the solution viscosity is 3500 Centipoise, the immersion time ranges from 5 to 30 min, and the coating thickness is 15 μm to 80 μm. In this embodiment, the optical fiber maintains a constant pull-out speed of 10 mm / min, the solution viscosity is 3500 Centipoise, the immersion time is 10 minutes, and the coating thickness is 50 ± 5 μm.

[0066] 4) Finally, the graphene-clad optical fiber coated with PDMS solution is fixed on a rotating motor, the rotating motor is turned on and runs at a constant speed, and the optical fiber is placed in a vacuum drying oven and vacuumed again for 1 hour to ensure complete contact between the solution and the graphene, and finally heated and cured at a heating temperature of 80°C for 8 hours to finally prepare an optical fiber bending sensor.

[0067] Embodiment 3: Testing method of optical fiber bending sensor capable of sensing different bending directions

[0068] The optical fiber bending sensor of the present invention combines the advantages of laser-induced graphene and the flexibility of optical fiber, converts the bending of the graphene-clad optical fiber into the change of the electrical properties of the graphene conductive short wire. When the graphene layer bends inward or outward, the conductive properties of the graphene layer change, thereby changing the resistance value at both ends of the graphene layer, thereby realizing the sensing of the bending. Each graphene conductive short wire in the optical fiber bending sensor has different sizes and electrical properties. When the graphene conductive short wire is subjected to mechanical deformation of bending inward or outward, the contact degree between the graphene materials will change, thereby changing the resistance value of the graphene conductive short wire, thereby realizing the measurement of the bending direction and bending angle.

[0069] like Figure 2 As shown in the figure, the asymmetric structure of the two graphene conductive short wires can be seen by observing the graphene layer on the cross section of the optical fiber bending sensor. Through the conductive silver glue electrodes, wires and real-time resistance monitoring equipment, the two non-contact conductive short wires can realize bending sensing monitoring in four directions: x, -x, y, and -y.

[0070] The optical fiber bending sensor prepared by the present invention can test the bending characteristics through a wired testing method or a wireless testing method.

[0071] 1) The wired test method is: use a wire to lead out the conductive silver glue electrode, use a resistance measuring device to measure the change in resistance value at both ends of at least two graphene conductive short wires in the graphene layer, and quantitatively analyze the bending angle based on the resistance change rate to achieve the measurement of multi-directional bending deformation. When the laser-induced graphene material is bent, its internal microstructure will change, and the degree of contact between the graphene materials will change. Specifically, when the graphene conductive short wires bend outward, the contact density between the graphene materials decreases, and the internal conductive path is reduced, making the transmission of electrons difficult, resulting in an increase in the resistance of the graphene conductive short wires; when the graphene conductive short wires bend inward, the graphene material is squeezed at the bending position, the density between the graphene materials increases, and the internal conductive path increases, which reduces the transmission barrier of electrons, resulting in a decrease in the resistance of the graphene conductive short wires.

[0072] The specific steps of the wired testing method are: use a wire to lead out the conductive silver glue electrode, and use a resistance measuring device to measure the change in resistance at both ends of the graphene conductive short wire under a bending test. Since the electrical properties of each graphene conductive short wire are different, the resistance values ​​at both ends of the graphene conductive short wire at different positions are different. Therefore, the bending direction can be determined by the initial resistance. For bending in one direction, when the optical fiber bends outward and inward, the resistance value will increase and decrease respectively, and different bending angles will reflect different resistance values. In this way, the bending direction and bending angle of the optical fiber can be analyzed to realize the wired testing method.

[0073] The wired test method is based on the wired measurement of the resistance change of the graphene layer under mechanical bending strain. The graphene layer is the sensing part of the bending sensor. When the optical fiber bending sensor is subjected to bending deformation, one side of the graphene is strained, resulting in an increase or decrease in the graphene conductive path, and then the resistance value at both ends of the graphene conductive short line changes. The resistance value measured by the electrodes at both ends of the graphene conductive short line is directly analyzed by using a resistance measuring device. Therefore, the resistance change rate is used to quantify the bending angle of each graphene conductive short line to achieve the measurement of multi-directional bending deformation.

[0074] 2) The wireless testing method is as follows: using the graphene conductive short wire as an antenna, leading out the conductive silver glue electrode by connecting the coaxial feeder, sending the antenna signal from the graphene conductive short wire to the outside world, using a highly sensitive signal receiving device to capture the electromagnetic wave signal emitted by the antenna, and indirectly measuring the bending degree of the antenna by analyzing the change in signal strength. Under different bending degrees, the impedance-electromagnetic radiation characteristics brought by the graphene conductive short wire will also change, thereby increasing or decreasing the signal transmission efficiency, and the signal strength at the receiving end will be enhanced or weakened accordingly.

[0075] The specific steps of the wireless testing method are as follows: the graphene conductive short wire is led out through the conductive silver electrode, and the coaxial feeder is connected to transmit the generated signal from the signal source (such as a transmitter) to the antenna (graphene conductive short wire) to the outside world. A highly sensitive signal receiving device (such as an RF receiver) is used to capture the electromagnetic wave signal emitted by the antenna. The optical fiber bending sensor has the excellent electrical and mechanical properties of graphene, as well as the improvement of the conductivity of the silver deposition layer and the stability under mechanical strain. When the antenna is bent, the signal strength at the receiving end will change. Specifically, bending will cause the contact of the graphene conductive layer material of the device to be close or sparse, affecting its conductive properties, and then affecting the electromagnetic radiation characteristics of the graphene conductive short wire. By analyzing the changes in signal strength, the degree of bending of the antenna can be indirectly measured.

[0076] The wireless testing method is based on the wireless signal measurement of the graphene layer and the silver deposition layer under mechanical bending strain. The graphene layer and the silver deposition layer on the optical fiber can be regarded as flexible antennas. Their electromagnetic radiation characteristics will vary under different bending conditions. The bending condition can be judged by monitoring the changes in the received wireless signal. Different graphene conductive short wires have different electromagnetic radiation characteristics, resulting in different initial signal strengths received when connected without bending, which is used to distinguish different bending directions, thereby realizing bending sensing of optical fibers in different directions.

[0077] Figure 3 This is a schematic diagram for explaining the multi-directional bending of the optical fiber bending sensor; Figure 4 A schematic diagram of the resistance value of the optical fiber bending sensor being used to distinguish directions; Figure 5 This is a schematic diagram of the resistance change rate in the direction when the optical fiber bending sensor is bent outward on one side. Figure 3 As shown in the bending diagram of the direction of the graphene conductive short line, the device is bent from the vertical and horizontal directions respectively, so the device can monitor the bending conditions in the four directions of x, y, -x, and -y; Figure 4 It is shown that when no bending occurs, the x-axis and y-axis directions can be distinguished by measuring the resistance of two short graphene conductive lines. Then, by the change of the resistance value, if the resistance value increases, it means that the optical fiber is bent outward in the vertical or horizontal direction; if the resistance value decreases, it means that the optical fiber is bent inward, thus determining the bending direction of the optical fiber. Figure 5 As shown, when the first graphene conductive short line 2 is bent outward, the rate of change of the resistance value shows a positive correlation, indicating that when bending outward, the contact degree of the graphene material on the optical fiber cladding decreases, causing an increase in the resistance value, and thus the resistance change rate shows a positive correlation.

[0078] Compared with sensing the bending characteristics of optical fiber based on the change of optical properties, the present invention uses the unique structure of laser-induced graphene layer and the change of electrical characteristics under mechanical strain to realize multi-directional bending sensing. The device can sense the bending of optical fiber through wired testing under the change of resistance value at both ends of graphene layer and silver deposition layer caused by bending strain and wireless testing under the change of wireless signal receiving strength caused by graphene layer and silver deposition layer caused by optical fiber bending. The device preparation process is simple, low cost, has no effect on the internal optical path of optical fiber, realizes photoelectric separation sensing, and can be used to prepare integrated devices based on optical fiber.

[0079] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the present invention itself. Various changes may be made to the form and details without departing from the spirit and scope of the present invention.

Claims

1. A multifunctional optical fiber capable of sensing different bending directions, characterized in that: It comprises a polyimide optical fiber and a silicone protective layer coated on the outside of the polyimide optical fiber; a graphene layer is provided on the cladding of the polyimide optical fiber; the graphene layer comprises a plurality of graphene conductive short wires which are arranged on the polyimide optical fiber cladding and are not in contact with each other, and the graphene conductive short wires are parallel to the optical axis of the polyimide optical fiber; the plurality of graphene conductive short wires are asymmetrically arranged on the cross section of the polyimide optical fiber, and the sizes and electrical characteristics of the graphene conductive short wires are different; a silver deposition layer is attached to the graphene layer; and conductive silver glue electrodes are coated on both ends of the graphene conductive short wires.

2. The multifunctional optical fiber according to claim 1, characterized in that: The size refers to the length and width of the graphene conductive short wire, and the electrical property refers to the resistance value and electromagnetic radiation property of the graphene conductive short wire.

3. The multifunctional optical fiber according to claim 1, characterized in that: There are at least two graphene conductive short lines.

4. The method for preparing the multifunctional optical fiber according to claim 1, characterized in that: The steps include: Step 1: Inducing the generation of a plurality of graphene conductive short wires of different sizes that do not touch each other at different positions of the polyimide optical fiber cladding parallel to the optical axis direction by laser; the plurality of graphene conductive short wires are asymmetrically arranged on the cross section of the polyimide optical fiber; Step 2: using electroplating to attach a layer of metallic silver to the surface of the graphene layer; Step 3: Apply conductive silver paste to both ends of the graphene conductive short wire as electrodes, and use a vacuum drying oven to evacuate and air-dry the conductive silver paste; Step 4: Encapsulate a silicone protective layer on the outside of the polyimide optical fiber.

5. The method for preparing the multifunctional optical fiber according to claim 4, characterized in that: In step 1, the laser induced generation method is: The polyimide fiber cladding is used as a carrier for preparing laser-induced graphene. A CO2 laser is used to induce high temperature to generate laser-induced graphene at the polyimide fiber cladding position along the optical axis of the fiber. After a short graphene conductive line is generated, the angle of the polyimide fiber is rotated along the optical axis of the fiber, the laser scanning parameters are adjusted, and the CO2 laser is used again to induce high temperature to generate the next short graphene conductive line. This method is performed multiple times to eventually form a graphene layer containing multiple short graphene conductive lines.

6. The method for preparing the multifunctional optical fiber according to claim 5, characterized in that: In the laser induced generation method, the laser scanning parameters are: the wavelength of the CO2 laser is 10.6 μm, the laser spot diameter at the focus is 50 μm, the laser power is 0.01-30 W, and the laser scanning speed is 1-1000 mm / s.

7. The method for preparing the multifunctional optical fiber according to claim 4, characterized in that: In step 2, the electroplating method is specifically as follows: The graphene conductive short wire is electroplated by an electrochemical deposition method, a silver metal layer is deposited on the graphene conductive short wire, and the thickness of the silver metal layer is adjusted by adjusting the electroplating parameters.

8. The method for preparing the multifunctional optical fiber according to claim 4, characterized in that The specific operations of step 4 are: The surface of the graphene optical fiber prepared in step three is coated with PDMS flexible material, and the PDMS material is cured by a vacuum drying oven and a rotating motor device; before coating, the graphene clad optical fiber is subjected to plasma treatment and silanization treatment.

9. The method for testing a multifunctional optical fiber according to claim 1, characterized in that: The optical fiber bending sensor tests the bending characteristics by a wired testing method or a wireless testing method.

10. The method for testing a multifunctional optical fiber according to claim 9, characterized in that: The wired testing method comprises: using a wire to lead out the conductive silver glue electrode, using a resistance measuring device to monitor the resistance values ​​at both ends of all graphene conductive short lines in the graphene layer in real time, when the graphene conductive short line bends outward, the resistance of the graphene conductive short line increases; when the graphene conductive short line bends inward, the resistance of the graphene conductive short line decreases, and the bending angle is quantitatively analyzed based on the resistance change rate to achieve the measurement of multi-directional bending deformation; The wireless testing method is as follows: the conductive silver glue electrode is led out by connecting a coaxial feeder, a graphene conductive short wire is used as an antenna, an antenna signal is sent from the graphene conductive short wire to the outside world, a high-sensitivity signal receiving device is used to capture the electromagnetic wave signal emitted from the antenna, and the bending degree of the antenna is indirectly measured by analyzing the change in signal strength; under different bending degrees, the electromagnetic radiation characteristics brought by the graphene conductive short wire also change accordingly, thereby increasing or decreasing the signal transmission efficiency, and the signal strength at the receiving end is correspondingly enhanced or weakened.

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