A fiber-optic bend sensor with sensing different bend directions and a preparation method and a testing method thereof

Abstract

The application provides a fiber bending sensor with sensing different bending directions and a preparation method and a test method thereof, and belongs to the technical field of sensors.The fiber bending sensor comprises a polyimide optical fiber and a silica gel protective layer coated on the outer side of the polyimide optical fiber; a graphene layer is arranged on the cladding layer of the polyimide optical fiber; the graphene layer comprises a plurality of graphene conductive short lines which are not in contact with each other and are arranged on the cladding layer of the polyimide optical fiber, and the graphene conductive short lines are parallel to the optical axis of the polyimide optical fiber; the plurality of graphene conductive short lines are asymmetrically arranged on the cross section of the polyimide optical fiber, and the sizes and electrical properties of the graphene conductive short lines are different; a silver deposition layer is attached to the graphene layer; and both ends of the graphene conductive short lines are coated with conductive silver glue electrodes.The application can realize bending sensing in multiple directions, and has the advantages of low preparation cost, simple preparation process, high preparation efficiency and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sensors, and specifically relates to a fiber-optic bending sensor capable of sensing different bending directions and a preparation method and a testing method thereof. BACKGROUND

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

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

[0004] Technical scheme: The application discloses a multifunctional optical fiber capable of sensing different bending directions, comprising a polyimide optical fiber and a silica gel protective layer coated on the outer side of the polyimide optical fiber; a graphene layer is arranged on the cladding layer of the polyimide optical fiber; the graphene layer comprises a plurality of graphene conductive short lines arranged on the cladding layer of the polyimide optical fiber and not in contact with each other, and the graphene conductive short lines are parallel to the optical axis of the polyimide optical fiber; the plurality of graphene conductive short lines are asymmetrically arranged on the cross section of the polyimide optical fiber, and the size and electrical properties of the graphene conductive short lines are different; a silver deposition layer is attached to the graphene layer; and the two ends of the graphene conductive short lines are coated with conductive silver adhesive electrodes.

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

[0006] Further, the graphene conductive short line is at least two.

[0007] Further, the silica gel protective layer is a PDMS protective layer.

[0008] The application discloses a preparation method of the multifunctional optical fiber with the perception of different bending directions.

[0009] Step one: generating a plurality of graphene conductive short lines with different sizes and electrical properties by laser induction at different positions of the polyimide fiber cladding parallel to the optical axis direction; the plurality of graphene conductive short lines are asymmetrically arranged on the cross section of the polyimide fiber.

[0010] Step two: attaching a layer of silver metal on the surface of the graphene layer by using an electroplating method.

[0011] Step three: coating the two ends of the graphene conductive short line as electrodes by using conductive silver glue, and performing vacuumizing and air drying solidification on the conductive silver glue electrode by using a vacuum drying box.

[0012] Step four: encapsulating a silica gel protective layer on the outside of the polyimide fiber.

[0013] Further, in step one, the laser induction generation method is as follows:

[0014] using the polyimide fiber cladding as a carrier for preparing laser-induced graphene, generating laser-induced graphene by using a CO2 laser along the optical axis of the fiber at the position of the polyimide fiber cladding, after generating a graphene conductive short line, rotating the angle of the polyimide fiber along the optical axis of the fiber, adjusting the laser scanning parameters, and then using the CO2 laser for high-temperature induction to generate the next graphene conductive short line; in this way, the process is performed for multiple times, and finally a graphene layer containing a plurality of graphene conductive short lines is formed.

[0015] Further, in the laser induction generation method, the laser scanning parameters are as follows: the wavelength of the CO2 laser is 10.6 μm, the laser spot diameter at the focal point 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 two, the electroplating method is as follows:

[0017] the graphene conductive short line is electroplated by using an electrochemical deposition method, a silver metal layer is deposited on the graphene conductive short line, 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 0.001 A-0.004 A, the electroplating time is 10-30 minutes, and the thickness of the generated silver metal layer is 20-40 μm.

[0019] Further, in step three, the temperature of the vacuum drying box is set to 60℃, and the heating time is 20 minutes.

[0020] Further, in step four, the thickness of the silica gel protective layer is in the range of 20-80 mu m.

[0021] Further, the specific operation of step four is: coating the prepared graphene optical fiber surface with PDMS flexible material, and curing the PDMS material through a vacuum drying box and a rotary motor device.

[0022] Further, in step four, the graphene cladding optical fiber is subjected to plasma treatment and silanization treatment before coating.

[0023] The application also discloses a test method of the fiber bending sensor with the sensing function of different bending directions, and the bending characteristics are tested by a wired test method or a wireless test method.

[0024] Further, in the wired test method, the conductive silver adhesive electrode is led out by using a wire, and the resistance values of both ends of all graphene conductive short lines of the graphene layer are monitored in real time by using a resistance measuring device; when the graphene conductive short line is bent outward, the resistance of the graphene conductive short line increases; when the graphene conductive short line is bent inward, the resistance of the graphene conductive short line decreases; the bending angle is quantitatively analyzed based on the resistance change rate, and the measurement of multi-directional bending deformation is realized.

[0025] Further, in the wireless test method, the conductive silver adhesive electrode is led out by connecting a coaxial feeder, the graphene conductive short line is used as an antenna, the antenna signal is sent to the outside from the graphene conductive short line, 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 of the signal strength; under different bending degrees, the electromagnetic radiation characteristics of the graphene conductive short line also change, and then the signal transmission efficiency is increased or decreased, and the signal strength of the receiving end is correspondingly enhanced or weakened.

[0026] The application has the following advantages:

[0027] 1) The application can realize multi-directional bending sensing, and has low preparation cost, simple preparation process and high preparation efficiency.

[0028] 2) The application uses the laser-induced graphene technology to prepare the sensing part of the bending sensor, can prepare the graphene sensing unit without a mask, and uses the PDMS flexible material for curing and packaging.

[0029] 3) The application coats silver on the graphene conductive short line to reduce the resistance value and enhance the surface performance of the graphene layer under bending strain.

[0030] 4)The application combines laser-induced graphene and optical fiber, uses the excellent electrical properties of graphene layer and the arbitrary direction bending of optical fiber, solves the disadvantage that the optical fiber bending sensor can only fix the angle of single direction bending, widens the application scene of laser-induced graphene in the optical fiber bending sensor, and has great application prospect in the fields of bending sensing and electrical signal transmission. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a structural schematic diagram of the optical fiber bending sensor with sensing different bending directions in embodiment 1;

[0032] wherein, polyimide optical fiber-1, first graphene conductive short line-2, second graphene conductive short line-3, silver deposition layer-4, conductive silver adhesive electrode-5, silica gel protective layer-6;

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

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

[0035] Figure 4 is a schematic diagram of the resistance values of two graphene conductive short lines of the optical fiber bending sensor in embodiment 3 for distinguishing directions;

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

[0037] The technical scheme of the application will be described in detail by embodiments below, but the protection scope of the application is not limited to the embodiments.

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

[0039] As Figure 1As shown, the optical fiber bending sensor prepared in the embodiment includes a polyimide optical fiber 1 and a silica gel protective layer 6 wrapped outside the polyimide optical fiber. The polyimide optical fiber 1 is provided with a graphene layer on the cladding, the graphene layer includes two graphene conductive short lines arranged on the cladding of the polyimide optical fiber 1 and not in contact with each other, and the two graphene conductive short lines are parallel to the optical axis of the polyimide optical fiber. The two graphene conductive short lines are asymmetrically arranged on the cross section of the polyimide optical fiber 1, and the size and electrical properties of the graphene conductive short lines are different. The size difference refers to the difference in length and width of the graphene conductive short lines, and the electrical property difference refers to the difference in resistance value and electromagnetic radiation characteristics of the graphene conductive short lines. The two graphene conductive short lines are respectively a first graphene conductive short line 2 and a second graphene conductive short line 3. The graphene layer is attached with a silver deposition layer 4, and the two ends of the graphene conductive short line are coated with a conductive silver electrode 5.

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

[0041] The preparation method is as follows:

[0042] Step one, laser-induced generation of two graphene conductive short lines with different sizes and electrical properties on different positions of the polyimide optical fiber cladding parallel to the optical axis direction; a plurality of the graphene conductive short 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, a polyimide optical fiber is selected as the laser-induced graphene sensing part substrate, the diameter of the polyimide optical fiber is 180 microns, the thickness of the polyimide layer is 55 microns, and a straight line pattern for forming the graphene conductive short line is drawn by the laser control software of the upper computer;

[0045] 2) Place the optical fiber under the red light indication line of the CO2 laser, align the optical fiber with the red light indication line, and control the upper computer software to use the CO2 laser to induce the generation of a graphene layer on the polyimide optical fiber cladding (polyimide film). The specific operation is as follows: after generating a graphene conductive short line along the optical axis direction using the CO2 laser, rotate 90° along the optical axis, the purpose is to form an asymmetric structure of the graphene conductive short line on the 360° cladding of the optical fiber, and at the same time, change the CO2 laser parameters to distinguish the bending in different directions, and then prepare another graphene conductive short line on the optical fiber cladding.

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

[0047] In this embodiment, the first graphene conductive short line 2 has a length of 3 cm and a short line width of 110 μm; the second graphene conductive short line 3 has a length of 2.5 cm and a short line width of 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 fiber cladding, and the graphene layers of the two laser markings are not in contact. 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, and the scanning power is low, and the carbonization degree is low, so the resistance of the first graphene conductive short line is larger than that of the second conductive short line, as shown in FIG. 2B, so as to distinguish the sensing in different directions. At the same time, the preparation of the graphene conductive short line at 0° and 90° ensures the asymmetry of the structure. Figure 4

[0049] The graphene layer is adjusted by rotating the optical fiber along the optical axis to change the high-temperature induction position of the CO2 laser, and the parameters (laser scanning speed, laser scanning power, etc.) of the CO2 laser high-temperature induction are changed to generate two graphene conductive short lines at different positions. The electrical properties of each graphene conductive short line are different. The polyimide fiber cladding serves as a carrier for the growth of laser-induced graphene, combining the electrical properties of graphene with the arbitrary-angle bendability of the fiber. In this embodiment, the CO2 laser is used to generate two laser-induced graphene conductive short lines on the polyimide fiber cladding at different positions parallel to the optical axis. Due to the different laser induction parameters (laser scanning speed, laser power) of each graphene conductive short line, the sizes of the graphene conductive short lines are different, the electrical properties are different, and the asymmetry of the graphene on the fiber cladding is ensured.

[0050] Step two: a layer of silver metal is attached to the surface of the graphene layer using electroplating.

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

[0052] In this embodiment, the current size is set to 0.0015 A and the electroplating time is 20 minutes when electroplating silver on the two graphene conductive short lines. The silver layer has a thickness of 30 μm. The two graphene conductive short lines are electroplated separately, and the electroplating parameters are the same. Due to the different resistances of the graphene conductive short lines, the density of the silver particles in the corresponding silver layer is different, and the thickness of the silver layer is about 20-40 μm.

[0053] The specific operation of step two is:​

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

[0055] The plating solution is placed in a constant temperature water bath set at a certain temperature. The graphene conductive short line working electrode is placed in the plating solution, and the constant current state between the cathode and the anode is maintained. The thickness of the silver deposition layer is controlled by setting the current size and electroplating time through the electrochemical workstation. After electroplating is completed, the electroplated graphene conductive short line sample is taken out and washed thoroughly with deionized water to remove residual plating solution. Then, the sample is placed in a drying oven for drying treatment, and the electroplating step is finally completed. Through the above steps, a silver layer can be successfully deposited on the surface of the graphene conductive short line, improving the electrical properties of the graphene layer and enhancing the surface performance.

[0056] The plating solution is prepared by selecting 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 (concentration of 250 g / L), potassium metabisulfite (concentration of 45 g / L) and silver nitrate (concentration of 45 g / L). First, under stirring conditions, the potassium metabisulfite solution is added dropwise to the silver nitrate solution, at which time a turbid liquid with white precipitate is formed. Then, continue to add sodium thiosulfate to the turbid liquid under stirring conditions, and finally a slightly yellow and transparent solution can be obtained. Finally, brightener and anode activator are added to the solution to complete the preparation of the plating solution. The ratio of the brightener is nicotinic acid 4 g / L and polyethyleneimine 0.08 g / L, and the anode activator is thiosemicarbazide with a concentration of 0.6 g / L.

[0057] Step three, use conductive silver glue to coat both ends of the graphene conductive short line as conductive silver glue electrodes, and use a vacuum drying oven to vacuum and air dry the conductive silver glue electrodes. The conductive silver glue is purchased from Shenzhen Luxiansi Technology Co., Ltd., the temperature of the vacuum drying oven is set to 60°C, and the heating time is 20 minutes.

[0058] Step four, finally encapsulate a layer of silicone protective layer on the outside of the polyimide optical fiber.

[0059] The graphene optical fiber cladding is uniformly coated with PDMS flexible material using the pulling method, and the PDMS material is solidified by a vacuum drying oven and a rotary motor device.

[0060] The silicon gel protective layer uses PDMS (polydimethylsiloxane material) flexible material, the silver-coated graphene optical fiber is immersed in the PDMS solution, the PDMS flexible material is uniformly coated on the optical fiber cladding by using the pulling method, and the PDMS material is solidified by using a vacuum drying box and a rotary motor device. By coating PDMS, the graphene layer can be protected to prevent physical wear and tear of the graphene layer from falling off. The polyimide coated optical fiber is purchased from Nanjing Jingchu Optical Technology Co., Ltd., and the PDMS material is purchased from Dow Corning Corporation, USA.

[0061] The specific operation of step four is:

[0062] 1) The graphene cladding optical fiber is encapsulated using PDMS flexible polymer material, the base material and curing agent of PDMS are in a ratio of 10:1, and the laboratory balance is used for weighing. After the ratio is prepared, the PDMS solution is placed in a vacuum drying box for vacuum operation to remove the bubbles existing in the prepared solution;

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

[0064] 3) The optical fiber is slowly immersed in the PDMS solution which has been vacuumed, and then the optical fiber is pulled out of the solution at a constant speed. By controlling the pulling speed, the viscosity of the solution and the immersion time of the optical fiber, the thickness of the coating can be controlled. Generally, slower pulling speed will form thicker coating, and faster speed will form thinner coating.

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

[0066] 4) Finally, the graphene cladding optical fiber coated with PDMS solution is fixed on the rotary motor, the rotary motor is started at a constant speed and placed in the vacuum drying box for vacuum operation again for 1 hour to ensure that the solution is in complete contact with the graphene, and finally the heating and curing are carried out, the heating temperature is 80℃, and the time is 8 hours, and finally the optical fiber bending sensor is prepared.

[0067] Example 3: Test method for fiber optic bending sensor with different bending directions

[0068] The fiber optic bending sensor of this invention combines the flexibility of laser-induced graphene and optical fiber, transforming the bending of the graphene-clad fiber into a change in the electrical properties of the graphene conductive short wires. When the graphene layer bends inward or outward, its conductivity changes, thereby altering the resistance at both ends of the graphene layer and achieving bending sensing. Each graphene conductive short wire in the fiber optic bending sensor has a different size and electrical properties. The mechanical deformation of these short wires during inward or outward bending causes changes in the contact between the graphene materials, thus altering the resistance of the short wires and enabling the measurement of the bending direction and angle.

[0069] like Figure 2 As shown, observing the graphene layer in the cross-section of the fiber optic bending sensor reveals an asymmetrical structure of two short conductive graphene lines. By connecting the two non-contact conductive lines to a real-time resistance monitoring device via conductive silver paste electrodes, wires, and the sensor, bending sensing and monitoring in four directions (x, -x, y, -y) can be achieved.

[0070] The fiber optic bending sensor prepared by this invention can be used to test bending characteristics using either wired or wireless testing methods.

[0071] 1) The wired testing method is as follows: Conductive silver paste electrodes are led out using wires. A resistance measuring device is used to measure the resistance change at both ends of at least two short conductive graphene lines in the graphene layer. The bending angle is quantitatively analyzed based on the resistance change rate, achieving multi-directional bending deformation measurement. When laser-induced graphene material is bent, its internal microstructure changes, and the degree of contact between graphene materials changes. Specifically, when the short conductive graphene lines bend outwards, the contact density between graphene materials decreases, reducing internal conductive pathways and making electron transport more difficult, leading to an increase in the resistance of the short conductive graphene lines. When the short conductive graphene lines bend inwards, the graphene material is compressed at the bending position, increasing the density between graphene materials and increasing internal conductive pathways, reducing the resistance to electron transport and leading to a decrease in the resistance of the short conductive graphene lines.

[0072] The specific steps of the wired test method are as follows: the conductive silver electrode is led out by using a wire, and the resistance value change of the graphene conductive short line is measured by using a resistance measuring device under bending test. Since the electrical characteristics of each graphene conductive short line are different, the resistance values of the graphene conductive short line at different positions are different, so the bending direction can be judged by the initial resistance. For a bending direction, when the optical fiber bends outward and outward, the resistance value will increase and decrease respectively, and different bending angles will result in different resistance values, so as to analyze the bending direction and bending angle of the optical fiber, and realize the wired test method.

[0073] The wired test method is based on the wired measurement method of the resistance value change of the graphene layer under mechanical bending strain. The graphene layer serves as the sensing part of the bending sensor. When the optical fiber bending sensor is subjected to bending deformation, the graphene side is subjected to strain, which causes the increase or decrease of the graphene conductive path, and then the resistance value of the graphene conductive short line changes. The resistance value of the graphene conductive short line is directly analyzed by using a resistance measuring device. Therefore, the bending angle of each graphene conductive short line is quantitatively analyzed by using the resistance change rate, and the measurement of multi-directional bending deformation is realized.

[0074] 2) The wireless test method is as follows: the graphene conductive short line is used as an antenna, the conductive silver electrode is led out by connecting a coaxial feeder, the antenna signal is sent to the outside from the graphene conductive short line, and a high-sensitivity signal receiving device is used to capture the electromagnetic wave signal emitted by the antenna. By analyzing the change of signal strength, the bending degree of the antenna can be indirectly measured. Under different bending degrees, the impedance-electromagnetic radiation characteristics of the graphene conductive short line also change, and then the signal transmission efficiency is increased or decreased, and the receiving end signal strength is correspondingly enhanced or weakened.

[0075] The specific steps of the wireless test method are as follows: the graphene conductive short line is led out by the conductive silver electrode, and the generated signal is transmitted from the signal source (such as a transmitter) to the antenna (graphene conductive short line) for emission to the outside through the connection of a coaxial feeder. A high-sensitivity 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 excellent electrical and mechanical properties of graphene and the stability of the silver deposition layer under mechanical strain. When the antenna is bent, the receiving end signal strength will change. Specifically, bending will cause the graphene conductive layer material of the device to be in close contact or sparse, affecting its conductivity, and then affecting the electromagnetic radiation characteristics of the graphene conductive short line. By analyzing the change of signal strength, the bending degree of the antenna can be indirectly measured.

[0076] The wireless test 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 a flexible antenna. The electromagnetic radiation characteristics of the flexible antenna will have different performances under different bending conditions. By monitoring the changes of the received wireless signal, the bending condition can be determined. Different graphene conductive short lines have different electromagnetic radiation characteristics, resulting in different initial signal strengths received under unbending conditions. The different graphene conductive short lines are used to distinguish different bending directions, so as to realize the bending sensing of the optical fiber in different directions.

[0077] Figure 3 is a schematic diagram for illustrating the multi-directional bending of the optical fiber bending sensor. Figure 4 is a schematic diagram for illustrating the resistance value of the optical fiber bending sensor for distinguishing the directions. Figure 5 is a schematic diagram for illustrating the resistance change rate in the direction of the optical fiber bending sensor when bending outward in one direction. As shown in the figure, Figure 3 is a schematic diagram for illustrating the bending of the graphene conductive short line in the direction. The bending is performed from the vertical and horizontal directions, respectively. Therefore, the device can monitor the bending conditions in the x, y, -x, and -y directions. As shown in the figure, Figure 4 is a schematic diagram for illustrating that the x and y axis directions can be distinguished by measuring the resistance values of the two graphene conductive short lines under no bending change. The bending direction of the optical fiber can be determined by the resistance value change. If the resistance value increases, it indicates that the optical fiber bends outward in the vertical or horizontal direction. If the resistance value decreases, it indicates that the optical fiber bends inward, so as to determine the bending direction of the optical fiber. Figure 5 As shown in the figure, the resistance value change rate of the first graphene conductive short line 2 is positively correlated when the first graphene conductive short line 2 is bent outward in the direction. It indicates that the contact degree of the graphene material on the optical fiber cladding decreases when the optical fiber bends outward, causing the increase of the resistance value, so that the resistance change rate is positively correlated.

[0078] Compared with the bending sensing of the optical fiber based on the change of the optical properties, the present application can realize multi-directional bending sensing by using the unique structure of the laser-induced graphene layer and the change of the electrical properties under mechanical strain. The device can sense the bending of the optical fiber by the wired test method based on the resistance value change of the graphene layer and the silver deposition layer and the wireless test method based on the change of the received wireless signal strength of the graphene layer and the silver deposition layer caused by the bending of the optical fiber. The device has a simple preparation process, low cost, no influence on the internal optical path of the optical fiber, realizes photoelectric separation sensing, and can be used for preparing an integrated device based on the optical fiber.

[0079] As described above, although the present application has been shown and described with reference to specific preferred embodiments, it is not to be construed as being in any way limited to the details shown and described. Various modifications in form and details can be made therein without departing from the spirit and scope of the application.

Claims

1. A multi-functional optical fiber having a sense of different bending directions, characterized by, The polyimide optical fiber includes a polyimide optical fiber and a silica gel protective layer coated outside the polyimide optical fiber; the cladding of the polyimide optical fiber is provided with a graphene layer; the graphene layer includes a plurality of graphene conductive short lines arranged on the cladding of the polyimide optical fiber and not in contact with each other, the graphene conductive short lines are parallel to the optical axis of the polyimide optical fiber; the plurality of graphene conductive short lines are asymmetrically arranged on the cross section of the polyimide optical fiber, and the sizes and electrical properties of the graphene conductive short lines are different; the graphene layer is attached with a silver deposition layer; and the two ends of the graphene conductive short lines are coated with conductive silver glue electrodes.

2. The multifunctional optical fiber according to claim 1, wherein, The sizes refer to the length and width of the graphene conductive short lines, and the electrical properties refer to the resistance value and electromagnetic radiation characteristics of the graphene conductive short lines.

3. The multifunctional optical fiber according to claim 1, wherein, The graphene conductive short lines are at least two.

4. The method for fabricating the multifunctional optical fiber according to claim 1, characterized in that, The method comprises the following steps: Step one, laser-induced generation of a plurality of graphene conductive short lines of different sizes at different positions of the polyimide optical fiber cladding parallel to the optical axis direction; the plurality of graphene conductive short lines are asymmetrically arranged on the cross section of the polyimide optical fiber; Step two, a layer of silver is attached to the surface of the graphene layer by electroplating; Step three, conductive silver glue is coated on the two ends of the graphene conductive short lines as electrodes, and vacuum drying and air drying of the conductive silver glue are performed by using a vacuum drying oven; Step four, a layer of silica gel protective layer is encapsulated outside the polyimide optical fiber.

5. The method for preparing the multifunctional optical fiber according to claim 4, characterized in that, In step one, the laser-induced generation method is as follows: The polyimide optical fiber cladding is used as a carrier for preparing laser-induced graphene, a CO2 laser is used to induce generation of laser-induced graphene at a high temperature along the optical axis of the optical fiber at the position of the polyimide optical fiber cladding, after a graphene conductive short line is generated, the angle of the polyimide optical fiber is rotated along the optical axis of the optical fiber, the laser scanning parameters are adjusted, and the next graphene conductive short line is induced to be generated by using the CO2 laser at a high temperature again; the above process is repeated for multiple times, and finally a graphene layer containing a plurality of graphene conductive short lines is formed.

6. The method of claim 5, wherein the multi-functional optical fiber is prepared by the steps of: In the laser-induced generation method, the laser scanning parameters are as follows: the wavelength of the CO2 laser is 10.6 μm, the laser spot diameter at the focal point 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 two, the electroplating method is as follows: An electrochemical deposition method is used to electroplate the graphene conductive short lines, a silver metal layer is deposited on the graphene conductive short lines, 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... In step four, the specific operation is as follows: A PDMS flexible material is coated on the surface of the graphene optical fiber prepared in step three, and the PDMS material is solidified by using a vacuum drying oven and a rotary motor device; before coating, the graphene cladding optical fiber is subjected to plasma treatment and silanization treatment.

9. The method of testing a multi-functional optical fiber of claim 1, wherein, The fiber bending sensor is tested for bending characteristics by using a wired test method or a wireless test method.

10. The test method of the multifunctional optical fiber according to claim 9, wherein The wired test method is that the conductive silver electrode is led out by a wire, the resistance values of both ends of all graphene conductive short lines of the graphene layer are monitored in real time by using a resistance measuring device, the graphene conductive short line resistance increases when the graphene conductive short line bends outward, the graphene conductive short line resistance decreases when the graphene conductive short line bends inward, the bending angle is quantitatively analyzed based on the resistance change rate, and the measurement of multi-directional bending deformation is realized. The wireless test method is that the conductive silver electrode is led out through a connected coaxial feeder, the graphene conductive short line is used as an antenna, the antenna signal is sent to the outside from the graphene conductive short line, the high-sensitivity signal receiving device is used to capture the electromagnetic wave signal emitted from the antenna, the bending degree of the antenna is indirectly measured by analyzing the change of the signal strength; under different bending degrees, the electromagnetic radiation characteristics brought by the graphene conductive short line also change, and then the signal transmission efficiency is increased or decreased, and the receiving end signal strength is correspondingly enhanced or weakened.

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