Single-core optical fiber, sensing monitoring method and system, manufacturing method and bending measurement device

Abstract

The application discloses a single-core optical fiber, a manufacturing method, a sensing monitoring method and system, and a bending measuring device. The single-core optical fiber comprises a fiber core for transmitting an optical signal, a cross section to be measured is preset on the fiber core, and a plurality of fiber grating sensors are circumferentially distributed in the fiber core, and each fiber grating sensor is parallel to an axis of the fiber core. The plurality of fiber grating sensors have different central wavelengths. The plurality of fiber grating sensors comprise a first fiber grating sensor, a second fiber grating sensor, and a third fiber grating sensor. The first fiber grating sensor, the second fiber grating sensor, and the third fiber grating sensor are respectively located at a first position, a second position, and a third position of the cross section to be measured. The fiber grating sensors in the single-core optical fiber can be implanted into a structure to be measured without damage, and the fiber grating sensors can quickly realize curvature demodulation and three-dimensional sensing judgment. The single-core optical fiber has high precision in bending detection.

Description

Technical Field

[0001] This application relates to the field of fiber optic grating sensing technology, specifically to a single-core optical fiber, a sensing and monitoring method and system based on the single-core optical fiber, a manufacturing method for the single-core optical fiber, and a bending measurement device. Background Technology

[0002] Currently, the following two methods are used to detect the three-dimensional shape of the structure under test: (1) Using conventional circular symmetric optical fiber scalar measurement method. Conventional circular symmetric optical fiber has fiber grating sensors based on the core center symmetry set at two preset positions on the optical fiber. Using conventional circular symmetric optical fiber with multi-directional layout to monitor the vector change of the three-dimensional shape is greatly affected by the strain field deformation and temperature cross-sensitivity of the structure under test, resulting in low measurement accuracy. This method has limitations and cannot truly and accurately reflect the vector change of the three-dimensional shape of the structure. (2) Specially customized optical fiber bending sensor. The optical fiber is customized according to the special needs of the structure under test, which is expensive and has a weak ability to distinguish the vector change of the three-dimensional shape. Summary of the Invention

[0003] This application provides a single-core optical fiber, a sensing and monitoring method and system based on the single-core optical fiber, a manufacturing method for the single-core optical fiber, and a bending measurement device to solve the problem of low detection accuracy in existing methods for detecting the three-dimensional shape of the structure under test.

[0004] One aspect of this application provides a single-core optical fiber, comprising:

[0005] Fiber core, used for transmitting optical signals; the fiber core has a pre-set cross-section to be measured; and

[0006] Multiple fiber Bragg grating sensors are circumferentially distributed in the fiber core, with each fiber Bragg grating sensor parallel to the axis of the fiber core; each of the multiple fiber Bragg grating sensors has a different center wavelength; wherein, the multiple fiber Bragg grating sensors include a first fiber Bragg grating sensor, a second fiber Bragg grating sensor, and a third fiber Bragg grating sensor;

[0007] The first fiber optic sensor is located at the first position of the cross section to be measured;

[0008] The second fiber optic sensor is located at a second position on the cross-section to be measured;

[0009] The third fiber optic grating sensor is located at the third position of the cross section to be measured.

[0010] Optionally, the plurality of fiber Bragg grating sensors are uniformly distributed in the fiber core, and the plurality of fiber Bragg grating sensors are all close to the cladding of the single-core fiber, the cladding being fitted over the fiber core; a coating layer is fitted over the cladding.

[0011] Optionally, the single-core optical fiber is attached to the structure under test, and the bending direction of the plurality of fiber Bragg grating sensors follows the bending direction of the structure under test;

[0012] The distance between adjacent fiber Bragg grating sensors on the cross section to be measured is consistent.

[0013] Optionally, the distances from the first position, the second position, and the third position to the axis of the fiber core are the same.

[0014] Alternatively, each fiber Bragg grating sensor is fabricated point by point using a femtosecond laser.

[0015] Optionally, the center wavelengths of the plurality of fiber Bragg grating sensors are separated by at least 2 nanometers.

[0016] One aspect of this application provides a sensing and monitoring method based on a single-core optical fiber, including the single-core optical fiber described above, wherein the single-core optical fiber is attached to the structure under test; the method includes:

[0017] The working light source is received through one end of the single-core optical fiber;

[0018] The light intensity reflected by each fiber Bragg grating sensor from the working light source is obtained;

[0019] Based on the light intensity reflected by each fiber Bragg grating sensor, the bending direction and bending radius of the cross section to be measured are determined, thereby determining the bending direction and bending radius of the structure to be measured.

[0020] Optionally, determining the bending direction and bending radius of the cross-section to be measured based on the light intensity reflected by each fiber Bragg grating sensor further includes:

[0021] The strain-reflected light intensity peak value of the reflected light output by each fiber Bragg grating sensor on its respective cross-section to be measured is obtained, wherein the strain-reflected light intensity peak value is the maximum value of the light intensity of the reflected light output by the fiber Bragg grating sensor on its respective cross-section to be measured when strain occurs.

[0022] When the fiber Bragg grating sensor is in its initial state, the initial peak value of the reflected light intensity output by each fiber Bragg grating sensor on its respective cross section to be measured is obtained;

[0023] The mode field offset of each fiber Bragg grating sensor is obtained; the mode field offset of each fiber Bragg grating sensor is obtained by comparing the peak value of the strain reflected light intensity of the fiber Bragg grating sensor with the peak value of the initial reflected light intensity of the fiber Bragg grating sensor.

[0024] Obtain a first ratio of the peak strain-reflected light intensity of the first fiber Bragg grating sensor to the peak initial reflected light intensity, and a second ratio of the peak strain-reflected light intensity of the second fiber Bragg grating sensor to the peak initial reflected light intensity. Based on the first and second ratios, determine the bending direction of the cross-section to be measured.

[0025] The bending radius of the cross section to be measured is obtained based on the position of the third fiber grating sensor, the center position of the cross section to be measured, the bending direction, and the mode field offset of the third fiber grating sensor.

[0026] Optionally, obtaining a first ratio of the peak strain-reflected light intensity of the first fiber Bragg grating sensor to the peak initial reflected light intensity, and a second ratio of the peak strain-reflected light intensity of the second fiber Bragg grating sensor to the peak initial reflected light intensity, and obtaining the bending direction of the cross-section to be measured based on the first ratio and the second ratio, includes:

[0027] Based on the first ratio, two candidate positions are determined on the cross-section to be measured;

[0028] Based on the second ratio, one of the two candidate positions is determined as the target position; and

[0029] Based on the target position and the center position of the cross-section to be measured, the bending direction of the structure to be measured is determined to be a bending direction from the center position of the cross-section to be measured toward the target position.

[0030] Optionally, after determining the bending direction and bending radius of the cross-section to be measured, the method further includes:

[0031] The target three-dimensional shape of the structure under test is determined based on the bending direction, the bending radius, and the pre-constructed initial three-dimensional shape of the structure under test.

[0032] One aspect of this application provides a sensing and monitoring system based on a single-core optical fiber, including the single-core optical fiber described above, wherein the single-core optical fiber is attached to the structure to be tested.

[0033] The system includes:

[0034] The receiving module is used to receive the working light source through one end of the single-core optical fiber;

[0035] The acquisition module is used to acquire the light intensity reflected by each fiber Bragg grating sensor from the working light source;

[0036] The determination module is used to determine the bending direction and bending radius of the cross section to be measured based on the light intensity reflected by each fiber Bragg grating sensor, thereby determining the bending direction and bending radius of the structure to be measured.

[0037] One aspect of this application provides a method for manufacturing a single-core optical fiber, including the single-core optical fiber described above. The single-core optical fiber includes a core and a cladding and a coating layer surrounding and covering the core, the coating layer covering the outside of the cladding. The manufacturing method includes:

[0038] The single-core optical fiber is fixed on the optical fiber processing platform;

[0039] The single-core optical fiber is controlled to move at a preset speed on the optical fiber processing platform;

[0040] A femtosecond laser is output through the coating layer and the cladding layer to form a first fiber grating sensor at a first position in the fiber core, a second fiber grating sensor at a second position in the fiber core, and a third fiber grating sensor at a third position in the fiber core. The first, second, and third positions are all located at a predetermined distance from the center of the fiber core.

[0041] Optionally, the manufacturing method further includes:

[0042] The first, second, and third positions where the femtosecond laser etched the fiber core were confirmed using a charge-coupled device.

[0043] Optionally, the manufacturing method further includes:

[0044] By rotating the single-core optical fiber, the femtosecond laser can inscribe corresponding fiber optic grating sensors at the first, second, and third positions, respectively.

[0045] One aspect of this application provides a bending measuring device, characterized in that it includes:

[0046] A laser is used to output a working light source;

[0047] As described above, the single-core optical fiber includes multiple fiber Bragg grating sensors; the single-core optical fiber includes a core and multiple fiber Bragg grating sensors located on the core; the single-core optical fiber is used to: receive the working light source and output the light intensity reflected from the working light source through each fiber Bragg grating sensor; and

[0048] A controller is connected to the single-core optical fiber; the controller is used to: detect the light intensity transmitted by the single-core optical fiber, and perform bending measurement based on the light intensity.

[0049] This invention provides a single-core optical fiber, a sensing and monitoring method and system based on the single-core optical fiber, a manufacturing method for the single-core optical fiber, and a bending measurement device. The fiber grating sensor in the single-core optical fiber of this invention can be non-destructively implanted into the structure under test. The fiber grating sensor enables rapid curvature demodulation and three-dimensional sensing judgment, and the bending detection through the single-core optical fiber has high accuracy. By detecting the light intensity changes of the reflected light from the first, second, and third fiber grating sensors at each cross-section of the single-core optical fiber, the bending direction and bending radius of each cross-section in three-dimensional space are determined, effectively improving the bending detection accuracy of the structure under test. Attached Figure Description

[0050] The accompanying drawings are provided to further illustrate the present application and form part of the specification. They are used together with the embodiments of the present application to explain the application and do not constitute a limitation thereof. In the drawings:

[0051] Figure 1 The schematic diagram illustrates the structure of a single-core optical fiber according to an embodiment of this application;

[0052] Figure 2 The illustration shows a schematic diagram of multiple bending directions in a single-core optical fiber according to an embodiment of this application;

[0053] Figure 3 This illustration schematically shows the relationship between the reflected light intensity changes of three fiber Bragg grating sensors in a single-core optical fiber and the rotation angle in an embodiment of this application.

[0054] Figure 4 The flowchart illustrating an example of the steps of a sensing and monitoring method based on a single-core optical fiber according to an embodiment of the present invention is shown.

[0055] Figure 5 The schematic diagram illustrates an example flowchart of the steps for obtaining the bending direction and bending radius in the single-core optical fiber-based sensing and monitoring method of this application embodiment;

[0056] Figure 6 The schematic diagram illustrates an example flowchart of the step of determining the bending direction in the sensing and monitoring method based on a single-core optical fiber according to an embodiment of this application;

[0057] Figure 7 A block diagram of a single-core optical fiber-based sensing and monitoring system according to an embodiment of this application is shown schematically. Detailed Implementation

[0058] The preferred embodiments of this application are described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit this application.

[0059] Example 1

[0060] This application provides a single-core optical fiber, the single-core optical fiber comprising:

[0061] Fiber core 1, used for transmitting optical signals; the fiber core has a pre-set cross-section to be measured; and

[0062] Multiple fiber Bragg grating sensors are circumferentially distributed in the fiber core 1, with each fiber Bragg grating sensor parallel to the axis of the fiber core 1; each of the multiple fiber Bragg grating sensors has a different center wavelength; wherein, the multiple fiber Bragg grating sensors include a first fiber Bragg grating sensor, a second fiber Bragg grating sensor, and a third fiber Bragg grating sensor;

[0063] The first fiber optic sensor is located at the first position of the cross section to be measured;

[0064] The second fiber optic sensor is located at a second position on the cross-section to be measured;

[0065] The third fiber optic grating sensor is located at the third position of the cross section to be measured.

[0066] The center wavelengths of each fiber Bragg grating sensor are set to be at least 2 nm apart.

[0067] As an example, the plurality of fiber Bragg grating sensors are uniformly distributed in the fiber core 1, and all the plurality of fiber Bragg grating sensors are close to the cladding 2 of the single-core fiber, the cladding 2 being used to cover the outside of the fiber core 1; a coating layer 3 is provided on the outside of the cladding 2. Preferably, the plurality of fiber Bragg grating sensors are disposed at the boundary between the fiber core 1 and the cladding 2.

[0068] like Figure 1 As shown, a single-core optical fiber comprises a three-layer structure: a coating layer 3, a cladding layer 2, and a core 1. For example, the coating layer 3 can be a polymer plastic, and both the cladding layer 2 and the core 1 can be made of silicon dioxide. The refractive index of the core 1 is higher than that of the cladding layer 2; therefore, the working light source can propagate through total internal reflection in the core 1 at a preset propagation angle within the single-core optical fiber.

[0069] As an example, each fiber Bragg grating sensor is fabricated point by point using femtosecond lasers.

[0070] In this embodiment, the fiber grating sensor is fabricated in micro-nano dimensions on the core 1 of a single-core optical fiber. Multiple parallel fiber grating sensor structures are etched onto the edge of the fiber core 1 using a femtosecond laser. The fiber grating sensors are fabricated point-by-point using a femtosecond laser, with each fabricated point being less than 1 μm in size. The length of a single fiber grating sensor is greater than 1 mm, and each fiber grating sensor has an independent center wavelength. The coating layer 3 of the single-core optical fiber is not stripped during the sensor fabrication process, eliminating the need for a secondary coating process on the single-core optical fiber and enhancing the mechanical strength of the fabricated fiber grating sensor.

[0071] As an example, the single-core optical fiber is attached to the structure under test, and the bending direction of the plurality of fiber Bragg grating sensors follows the bending direction of the structure under test; the distance between adjacent fiber Bragg grating sensors on the cross section to be measured is consistent.

[0072] As an example, the distances from the first position, the second position, and the third position to the axis of the fiber core are the same.

[0073] In this embodiment, the angle between adjacent fiber Bragg grating sensors on the same cross-section to be measured is 60 degrees, that is, the three fiber Bragg grating sensors on each cross-section to be measured are arranged in an equilateral triangle, with the three fiber Bragg gratings located at the three vertices of the equilateral triangle; and the position of each fiber Bragg grating sensor is located on the fiber core 1 near the boundary of the cladding 2.

[0074] Example 2

[0075] Please see Figure 4 This document illustrates a flowchart of the sensing and monitoring method based on a single-core optical fiber according to an embodiment of the present invention. The single-core optical fiber is the same as described in the above embodiment, and includes a fiber core. It is understood that the flowchart in this method embodiment is not intended to limit the order of execution steps. The following description uses a controller as the execution entity, which can be a microcontroller, computer device, etc., as detailed below:

[0076] The single-core optical fiber is attached to the structure under test; a first fiber Bragg grating sensor is located at a first position of the cross-section to be measured, a second fiber Bragg grating sensor is located at a second position of the cross-section to be measured, and a third fiber Bragg grating sensor is located at a third position of the cross-section to be measured. Each fiber Bragg grating sensor is parallel to the normal of the cross-section to be measured; wherein, the normal of the cross-section to be measured is collinear with the axis of the fiber core; each fiber Bragg grating sensor has a different center wavelength. Figure 4 As shown, the sensing and monitoring method based on a single-core optical fiber may include steps S100 to S104, wherein:

[0077] Step S100: Control one end of the single-core optical fiber to receive the working light source.

[0078] For example, the working light source can be a laser with an emission wavelength of 520nm.

[0079] Step S102: Obtain the light intensity reflected by each fiber Bragg grating sensor from the working light source.

[0080] In this embodiment, light intensity represents the energy intensity of light reflected from the working light source by the fiber Bragg grating sensor onto the cross section to be measured. When the working light source achieves total internal reflection propagation within the single-core fiber at a preset propagation angle, the input working light source will form a certain energy intensity distribution on each cross section to be measured where the fiber Bragg grating sensor is located. The energy intensity distribution of light on the waveguide cross section is called the mode field. The mode field of a single-core fiber generally exhibits a normal Gaussian intensity distribution, with higher energy intensity in the center and lower energy intensity around the edges. It should be noted that in the initial state, i.e., the unbent state, the mode field reflected by the fiber Bragg grating sensor of the single-core fiber is symmetrically distributed around the center of the fiber core 1. Specifically, the energy exhibits a standard normal Gaussian distribution around the center point of the fiber core 1.

[0081] Step S104: Based on the light intensity reflected by each fiber Bragg grating sensor, determine the bending direction and bending radius of the cross section to be measured, and then determine the bending direction and bending radius of the structure to be measured.

[0082] In this embodiment, fiber Bragg grating sensors are respectively inscribed at the first, second, and third positions in the core 1 of the single-core optical fiber. The distances from the three fiber Bragg grating sensors on the same cross-section to be measured to the center of that cross-section are consistent, as are the distances between adjacent fiber Bragg grating sensors on the same cross-section. The angle between adjacent fiber Bragg grating sensors on the same cross-section is 60 degrees. The three fiber Bragg grating sensors on each cross-section are arranged in an equilateral triangle, with the three fiber Bragg gratings located at the three vertices of the triangle. Each fiber Bragg grating sensor is located on the fiber core 1 near the boundary of the cladding 2. In this embodiment, the data detected by the three fiber Bragg grating sensors arranged in an equilateral triangle exhibits more obvious regularity, making the subsequent bending detection results more accurate. Therefore, in this embodiment, the actual position after mode field shift can be obtained by comparing the reflected light intensity of the three fiber Bragg grating sensors, thereby obtaining the fiber bending direction. When the fiber at the location of the fiber Bragg grating sensor bends to a certain curvature, the direction of fiber bending is correlated with the relative intensity difference of the fiber Bragg grating sensors. The relative intensity difference can be understood as a mode field difference.

[0083] To improve the accuracy of optical fiber in measuring spatial orientation, please refer to [link / reference needed]. Figure 5 Step S104, which determines the bending direction and bending radius of the cross-section to be measured based on the light intensity reflected by each fiber Bragg grating sensor, may further include the following steps S200 to S208: Step S200, obtaining the strain-reflected light intensity peak value of the reflected light output by each fiber Bragg grating sensor on its respective cross-section to be measured, wherein the strain-reflected light intensity peak value is the maximum value of the light intensity of the reflected light output by the fiber Bragg grating sensor on its respective cross-section to be measured when strain occurs; Step S202, obtaining the initial reflected light intensity peak value of the reflected light output by each fiber Bragg grating sensor on its respective cross-section to be measured when the fiber Bragg grating sensor is in its initial state; Step S204, obtaining the mode field offset of each fiber Bragg grating sensor. The mode field offset of each fiber Bragg grating sensor is obtained by comparing the peak strain-reflected light intensity of the fiber Bragg grating sensor with its initial peak reflection light intensity. In step S206, a first ratio of the peak strain-reflected light intensity of the first fiber Bragg grating sensor to its initial peak reflection light intensity and a second ratio of the peak strain-reflected light intensity of the second fiber Bragg grating sensor to its initial peak reflection light intensity are obtained on the same cross-section to be measured. Based on the first and second ratios, the bending direction of the cross-section to be measured is obtained. In step S208, the bending radius of the cross-section to be measured is obtained based on the position of the third fiber Bragg grating sensor on the same cross-section to be measured, the center position of the same cross-section to be measured, the bending direction, and the mode field offset of the third fiber Bragg grating sensor. The initial state of the single-core fiber is an unbent state.

[0084] In this embodiment, the bending direction of the cross-section to be measured can be confirmed by two sensors on the cross-section to be measured. When the optical fiber bends, the center of the mode field of the fiber shifts away from the center of the fiber core 1. The larger the bending angle of the fiber, the greater the shift of the center of the mode field, and the mode field shift and the bending radius of the fiber exhibit a certain linear relationship. The mode field shift direction of the reflected light on the optical fiber will be reflected on the cross-section to be measured according to the bending direction of the fiber. Therefore, in the case of subsequent bending of the single-core optical fiber with the structure under test, the peak value of the strain-reflected light intensity reflected on the cross-section to be measured by the fiber Bragg grating sensor is obtained, and the difference between the peak value of the strain-reflected light intensity and its corresponding initial peak value is calculated to obtain the mode field shift.

[0085] For example, the bending radius of a single-core optical fiber can be determined using a third sensor on the same cross-section being measured; the bending radius can be obtained using the following formula:

[0086] R = (Ec - Ec0) * sinθ

[0087] Where R represents the bending radius, Ec represents the peak value of the strain-reflected light intensity of the third sensor in a strained and bent state, Ec0 represents the peak value of the initial reflected light intensity of the third sensor in the initial state, and θ represents the angle between the line connecting the third sensor and the center position of the cross section to be measured and the bending direction; by calculating the difference between the peak value of the strain-reflected light intensity of the third sensor and the peak value of the initial reflected light intensity, the mode field offset of the third sensor can be obtained; by substituting the mode field offset into the above formula, the bending radius of the cross section to be measured can be calculated.

[0088] In this embodiment, the ability of three fiber optic grating sensors on the same cross-section to autonomously sense direction, without relying on the mechanical model of the structure under test, enables the rapid, efficient, and accurate sensing of the spatial bending direction of the structure under test.

[0089] To quickly and accurately determine the bending direction of the optical fiber, please refer to [link / reference needed]. Figure 6 The bending direction can also be obtained through the following operations: step S300, determining two candidate positions on the cross-section to be measured according to the first ratio; step S302, determining one of the two candidate positions as the target position according to the second ratio; and step S304, determining the bending direction of the structure to be measured as bending from the center position of the cross-section to be measured toward the target position according to the target position and the center position of the cross-section to be measured.

[0090] Combination Figure 1 and Figure 2 As shown, taking the cross-section to be measured as an example, the first fiber Bragg grating sensor is fbg1, the second fiber Bragg grating sensor is fbg2, and the third fiber Bragg grating sensor is fbg3. The three fiber Bragg grating sensors are arranged in an equilateral triangle on the cross-section to be measured. A coordinate system is established on the cross-section to be measured, with the center of the cross-section as the origin, and the coordinates as shown... Figure 1The bending direction of the optical fiber is explained using the x-axis and y-axis as references. The position of fbg1 is defined as the first point, and the direction from the origin to the first point is defined as the first direction. Using the distance from fbg1 to the center of the cross-section to be measured as a reference distance, the position on the extension of the line connecting fbg2 and the origin, at a distance from the origin by a reference distance, is defined as the second point, and the direction from the origin to the second point is defined as the second direction. The position on the positive x-axis, at a distance from the origin by a reference distance, is defined as the third point, and the direction from the origin to the third point is defined as the third direction. The position of fbg3 is defined as the fourth point, and the direction from the origin to the fourth point is defined as... The fourth direction is defined as follows: the position on the negative y-axis that is a reference distance from the origin is defined as the fifth point, and the direction from the origin to the fifth point is defined as the fifth direction; the position of fbg2 is defined as the sixth point, and the direction from the origin to the sixth point is defined as the sixth direction; the position on the negative x-axis that is a reference distance from the origin is defined as the seventh point, and the direction from the origin to the seventh point is defined as the seventh direction; the position on the extension of the line connecting fbg3 and the origin that is a reference distance from the origin is defined as the eighth point, and the direction from the origin to the eighth point is defined as the eighth direction.

[0091] Using the origin and reference radius, the first arc is defined as the path from the first point through the second, third, and fourth points to the fifth point. Each position on the first arc corresponds to a first ratio. The range of the first ratio corresponding to the first arc is preset to 0.5 to 2. Specifically, when the optical fiber bends in the first direction, the first ratio is 0.5; when the optical fiber bends in the fifth direction, the first ratio is 2. The first ratio corresponding to the position on the first arc gradually increases from 0.5 to 2 along the direction from the first point to the fifth point.

[0092] Using the origin and reference radius, the arc from the fifth point through the sixth, seventh, and eighth points to the first point is defined as the second arc. Each position on the second arc corresponds to a first ratio. The range of the first ratio corresponding to the second arc is preset to 2 to 0.5. The first ratio corresponding to the position on the second arc gradually decreases from 2 to 0.5 along the direction from the fifth point to the first point.

[0093] Using the origin and a reference radius, the third arc is defined as the path from the second point through the third, fourth, and fifth points to the sixth point. Each position on the third arc corresponds to a second ratio, which is preset to a range of 0.5 to 2. Specifically, the second ratio is 0.5 when the fiber bends towards the second direction and 2 when it bends towards the sixth direction. The second ratio corresponding to a position on the second arc gradually increases from 0.5 to 2 along the direction from the second point to the sixth point. The third arc partially overlaps with both the first and second arcs.

[0094] Using the origin and a reference radius, the fourth arc is defined as the path from the sixth point through the seventh, eighth, and first points to the second point. Each position on the fourth arc corresponds to a second ratio, which is pre-set to range from 2 to 0.5. Specifically, the second ratio corresponding to a position on the fourth arc gradually decreases from 2 to 0.5 along the direction from the sixth point to the second point. The fourth arc partially overlaps with both the first and second arcs.

[0095] In this embodiment, two candidate positions are determined based on a calculated first ratio: one candidate position is on the first arc, and the other candidate position is on the second arc. Two more candidate positions are determined based on a second ratio: one candidate position is on the third arc, and the other is on the fourth arc. The location of the two overlapping candidate positions is determined as the target position. The direction from the origin to the target position is determined as the bending direction of the cross-section to be measured. The bending direction of the cross-section to be measured can be quickly and accurately located using the sensing capabilities of the first and second fiber Bragg grating sensors. It should be noted that in the strain-bending state of a single-core optical fiber, since the fiber is in its initial state and no prestress is applied, the wavelength change caused by the fiber bending is very small and can be ignored.

[0096] To more easily understand the relationship between the light intensity reflected from the working light source by the first, second, and third fiber grating sensors in a single-core optical fiber and the fiber bending; for example... Figure 3 As shown, the horizontal axis represents the degree of rotation, which can be understood as the degree of fiber bending. The vertical axis represents the normalized power, which can be understood as the value of a periodic function related to the light intensity reflected by the fiber Bragg grating sensor. The normalized power is achieved by limiting the value of this periodic function to a preset range, such as between 0 and 3000. Three fiber Bragg grating sensors (e.g., Figure 2 The fbg1, fbg2 and fbg3 shown exhibit periodic changes within the 360° range of fiber bending, and the periodic change functions of the three fiber grating sensors have a 120° hysteresis relationship.

[0097] Please see Figure 2 The following example illustrates the operation of a fiber Bragg grating sensor measuring the bending direction using the sensing capabilities of three fiber Bragg grating sensors (e.g., fbg1, fbg2, and fbg3) for different bending directions of an optical fiber. fbg1 is located at the first point, fbg2 at the sixth point, and fbg3 at the fourth point.

[0098] (1) In the case of fiber bending, if the intensity of the first reflected light of fbg1 increases and the intensity of the first reflected light of fbg2 and the intensity of the first reflected light of fbg3 decreases proportionally, then the bending direction of the fiber is determined to be the direction from the origin to the first point, and the fiber bends in the first direction.

[0099] (2) In the case of fiber bending, if the intensity of the first reflected light of fbg1 and the intensity of the first reflected light of fbg3 increase proportionally and the intensity of the first reflected light of fbg2 decreases, then the bending direction of the fiber is determined to be the direction from the origin to the second point, and the fiber bends in the second direction.

[0100] (3) In the case of fiber bending, if the intensity of the first reflected light of fbg3 increases and the intensity of the first reflected light of fbg1 and the intensity of the first reflected light of fbg2 decrease proportionally, then the bending direction of the fiber is determined to be the direction from the origin to the fourth point, and the fiber bends in the fourth direction.

[0101] (4) In the case of fiber bending, if the intensity of the first reflected light of fbg1 decreases, and the intensity of the first reflected light of fbg2 and the intensity of the first reflected light of fbg3 increase proportionally, then the bending direction of the fiber is determined to be the direction from the origin to the fifth point, and the fiber bends toward the fifth direction.

[0102] (5) In the case of fiber bending, if the intensity of the first reflected light of fbg2 increases and the intensity of the first reflected light of fbg1 and the intensity of the first reflected light of fbg3 decrease proportionally, then the bending direction of the fiber is determined to be the direction from the origin to the sixth point, and the fiber bends towards the sixth direction.

[0103] (6) In the case of fiber bending, if the intensity of the first reflected light of fbg3 decreases, and the intensity of the first reflected light of fbg1 and the intensity of the first reflected light of fbg2 increase proportionally, then the bending direction of the fiber is determined to be the direction from the origin to the eighth point, and the fiber bends toward the eighth direction.

[0104] In an exemplary embodiment, when the bending radius is constant, the first ratio and the second ratio differ when the optical fiber bends in different directions. For example, when the bending radius is constant, the first ratio when the optical fiber bends in the first direction is much smaller than the first ratio when the optical fiber bends in the second direction, and the second ratio when the optical fiber bends in the first direction is much smaller than the second ratio when the optical fiber bends in the second direction.

[0105] The method further includes: determining the target three-dimensional shape of the structure under test based on the bending direction, the bending radius, and the pre-constructed initial three-dimensional shape of the structure under test.

[0106] In this embodiment, an initial three-dimensional shape of the structure to be tested is constructed in advance based on the outline of the structure to be tested; the center position of each cross section to be tested after bending is determined according to the bending direction and bending radius of each cross section to be measured; and the target three-dimensional shape of the structure to be tested after bending is generated based on the parameters of the initial three-dimensional shape of the structure to be tested, the center position of each cross section to be measured after bending, the bending direction and the bending radius.

[0107] The sensing and monitoring method based on a single-core optical fiber in the embodiments of the invention has at least the following beneficial effects:

[0108] (1) Fiber grating sensors in single-core optical fibers have the characteristics of small size, light weight, strong anti-electromagnetic interference, passive and stable performance. They can be implanted into the interior of the structure under test without affecting the mechanical properties of the structure under test. They can quickly realize curvature demodulation and autonomous perception and diagnosis of three-dimensional shape, and can also meet the needs of structure perception and shape adaptive active control.

[0109] (2) The bending detection scheme based on single-core optical fiber in this embodiment is not affected by temperature. Therefore, the accuracy of bending detection of the structure under test using this scheme is higher, ensuring measurement accuracy.

[0110] (3) The embodiments of the present invention are based on the autonomous sensing direction capability of multiple fiber optic grating sensors, which do not depend on the mechanical model of the structure under test. They are highly versatile and can be applied to the bending detection of structures under test with different shapes.

[0111] Example 3

[0112] This application provides a sensing and monitoring system based on a single-core optical fiber, wherein the single-core optical fiber is the single-core optical fiber described in the above embodiments, and the single-core optical fiber includes a fiber core. The single-core optical fiber is attached to the structure under test; a cross-section to be measured is preset on the fiber core 1 of the single-core optical fiber. A first fiber grating sensor is provided at a first position of the cross-section to be measured, a second fiber grating sensor is provided at a second position of the cross-section to be measured, and a third fiber grating sensor is provided at a third position of the cross-section to be measured. Each fiber grating sensor is parallel to the normal of the cross-section to be measured, wherein the normal of the cross-section to be measured is collinear with the axis of the fiber core; each fiber grating sensor has a different center wavelength; please refer to [link to relevant documentation]. Figure 7 The system includes:

[0113] Receiver module 400 is used to control one end of the single-core optical fiber to receive the working light source;

[0114] The acquisition module 402 is used to acquire the light intensity of the working light source reflected by the fiber optic grating sensor onto the corresponding cross section to be measured;

[0115] The determination module 404 is used to determine the bending direction and bending radius of the cross section to be measured based on the light intensity reflected by each fiber Bragg grating sensor, and then determine the bending direction and bending radius of the structure to be measured.

[0116] In an exemplary embodiment, the system further includes a reconstruction module (unidentified) for determining the target three-dimensional shape of the structure under test based on the bending direction of each cross-section to be measured, the bending radius, and the pre-constructed initial three-dimensional shape of the structure under test.

[0117] In an exemplary embodiment, the determining module 404 is further configured to: obtain the strain-reflected light intensity peak value of the reflected light output by each fiber Bragg grating sensor on its respective cross-section to be measured, wherein the strain-reflected light intensity peak value is the maximum value of the light intensity of the reflected light output by the fiber Bragg grating sensor on its respective cross-section to be measured when strain occurs; obtain the initial reflected light intensity peak value of the reflected light output by each fiber Bragg grating sensor on its respective cross-section to be measured when the fiber Bragg grating sensor is in its initial state; obtain the mode field offset of each fiber Bragg grating sensor; the mode field offset of each fiber Bragg grating sensor is obtained by comparing the fiber Bragg grating... The peak value of the strain-reflected light intensity of the sensor and the peak value of the initial reflected light intensity of the fiber Bragg grating sensor are obtained; a first ratio of the peak value of the strain-reflected light intensity of the first fiber Bragg grating sensor to the peak value of the initial reflected light intensity and a second ratio of the peak value of the strain-reflected light intensity of the second fiber Bragg grating sensor to the peak value of the initial reflected light intensity are obtained on the same cross-section to be measured, and the bending direction of the cross-section to be measured is obtained based on the first ratio and the second ratio; and the bending radius of the cross-section to be measured is obtained based on the position of the third fiber Bragg grating sensor on the same cross-section to be measured, the center position of the same cross-section to be measured, the bending direction, and the mode field offset of the third fiber Bragg grating sensor.

[0118] In an exemplary embodiment, the determining module 404 is further configured to: determine two candidate positions on the cross-section to be measured according to the first ratio; determine one of the two candidate positions as a target position according to the second ratio; and determine the bending direction of the structure to be measured as bending from the center position of the cross-section to be measured toward the target position according to the target position and the center position of the cross-section to be measured.

[0119] Example 4

[0120] This application provides a method for manufacturing a single-core optical fiber, wherein the single-core optical fiber is the single-core optical fiber described in the above embodiments. The single-core optical fiber includes a core and a cladding and a coating layer surrounding and covering the core, the coating layer covering the outside of the cladding; the manufacturing method includes:

[0121] The single-core optical fiber is fixed on the optical fiber processing platform;

[0122] The single-core optical fiber is controlled to move at a preset speed on the optical fiber processing platform;

[0123] A femtosecond laser is output through the coating layer and the cladding layer to form a first fiber grating sensor at a first position in the fiber core, a second fiber grating sensor at a second position in the fiber core, and a third fiber grating sensor at a third position in the fiber core. The first, second, and third positions are all located at a predetermined distance from the center of the fiber core.

[0124] In an exemplary embodiment, the manufacturing method further includes: confirming the first, second, and third positions on the fiber core where the femtosecond laser is etched by the charge-coupled device.

[0125] In an exemplary embodiment, the manufacturing method further includes: rotating the single-core optical fiber to cause the femtosecond laser to inscribe corresponding fiber optic grating sensors at the first position, the second position, and the third position, respectively.

[0126] In this embodiment, a fiber optic grating sensor is processed using a fiber optic processing platform. This platform comprises a femtosecond laser, a power adjustment device, an optical path system, and an imaging system. The laser emitted from the femtosecond laser undergoes power adjustment, and the optical path is then controlled by an optical switch to open and close the path. This allows the power-adjusted laser to be reflected by a mirror, focused by the objective lens, and act on a single-core fiber placed on a three-dimensional adjustment stage for micro / nano-scale processing. The three-dimensional adjustment stage employs a high-precision electrically controlled displacement platform, enabling sub-micron precision displacement control. The imaging system is used to image the processed area and observe the processing effect. For example, the imaging system can be a CCD (Charge-coupled Device). A pair of fiber optic clamping devices are fixed on the three-dimensional adjustment platform to hold and fix the single-core fiber to be processed. These clamping devices have a 360-degree rotation function, allowing precise adjustment and rotation of the single-core fiber to obtain the desired processing surface according to processing requirements. To achieve 360-degree directional recognition of the optical fiber, three fiber Bragg grating sensors, fbg1, fbg2, and fbg3, are fabricated in three directions of fiber core 1. The specific fabrication operation is as follows: After fabricating one fiber Bragg grating sensor on a cross section to be measured at the first position, rotate 120 degrees to fabricate a second fiber Bragg grating sensor at the second position. After the second fiber Bragg grating sensor is fabricated, rotate 120 degrees to fabricate a third fiber Bragg grating sensor at the third position.

[0127] As an example, the single-core optical fiber is attached to the structure under test, and the bending direction of the plurality of fiber Bragg grating sensors follows the bending direction of the structure under test;

[0128] The first fiber Bragg grating sensor, the second fiber Bragg grating sensor, and the third fiber Bragg grating sensor on the cross section of the single-core optical fiber constitute the cross section to be measured, and the distance between adjacent fiber Bragg grating sensors on the same cross section to be measured is consistent.

[0129] As an example, the distances from the first position, the second position, and the third position to the axis of the fiber core 1 are the same.

[0130] Three fiber Bragg grating sensors are arranged in parallel on the same cross-section to be measured. The angle between adjacent fiber Bragg grating sensors on the same cross-section is 60 degrees, meaning the three sensors on the same cross-section form an equilateral triangle. Each fiber Bragg grating sensor is located on the fiber core 1 near the boundary of the cladding 2. In this embodiment, the data detected by the three fiber Bragg grating sensors arranged in an equilateral triangle exhibits a more obvious regularity, making the subsequent bending detection results more accurate.

[0131] Example 5

[0132] This application provides a bending measuring device, including:

[0133] A laser is used to output a working light source;

[0134] The single-core optical fiber described in the above embodiments includes a fiber core and a plurality of fiber Bragg grating sensors located on the fiber core. The single-core optical fiber is used for: receiving a working light source and outputting the light intensity reflected from the working light source through each fiber Bragg grating sensor; and a controller connected to the single-core optical fiber. The controller is used for: detecting the light intensity transmitted by the single-core optical fiber and performing bending detection based on the light intensity.

[0135] The controller includes a light intensity receiving unit and a processor unit. The light intensity receiving unit is used to receive the light intensity transmitted by the single-core optical fiber, identify the light intensity information, and send it to the processor unit. The processor unit is used to calculate and process the light intensity information transmitted by the optical fiber to obtain the bending direction and bending radius of the final detected cross-sectional position.

[0136] The specific implementation method for bending detection is the same as that of the single-core optical fiber sensing and monitoring method in Example 2, and will not be repeated here. Preferably, the single-core optical fiber is attached to the structure under test, and the bending direction of the plurality of fiber Bragg grating sensors follows the bending direction of the structure under test; the distance between adjacent fiber Bragg grating sensors on the cross-section to be measured is consistent. The bending measurement device can be used to measure the bending direction and bending radius of the structure under test at the cross-section to be measured.

[0137] Finally, it should be noted that the above are merely preferred embodiments of this application and are not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A sensing and monitoring method based on a single-core optical fiber, characterized in that, Includes a single-core optical fiber, which is attached to the structure under test; The single-core optical fiber includes: a fiber core for transmitting optical signals; a cross-section to be measured pre-set on the fiber core; and multiple fiber Bragg grating sensors, circumferentially distributed in the fiber core, each fiber Bragg grating sensor being parallel to the axis of the fiber core; each of the multiple fiber Bragg grating sensors has a different center wavelength; wherein, the multiple fiber Bragg grating sensors include a first fiber Bragg grating sensor, a second fiber Bragg grating sensor, and a third fiber Bragg grating sensor; The first fiber optic sensor is located at the first position of the cross section to be measured; The second fiber optic sensor is located at a second position on the cross section to be measured; The third fiber optic grating sensor is located at the third position of the cross section to be measured; The method includes: Control one end of the single-core optical fiber to receive the working light source; The light intensity reflected by each fiber Bragg grating sensor from the working light source is obtained; The peak value of the strain-reflected light intensity of the reflected light output by each fiber Bragg grating sensor at the cross section to be measured under strain conditions is obtained. With the fiber Bragg grating sensor in its initial state, the initial peak value of the reflected light intensity output by each fiber Bragg grating sensor on its respective cross section to be measured is obtained; The mode field offset of each fiber optic grating sensor is obtained by comparing the peak value of strain reflected light intensity with the peak value of initial reflected light intensity. Obtain a first ratio of the peak strain-reflected light intensity of the first fiber Bragg grating sensor to the peak initial reflected light intensity, and a second ratio of the peak strain-reflected light intensity of the second fiber Bragg grating sensor to the peak initial reflected light intensity. Based on the first ratio, two candidate positions are determined on the cross-section to be measured; Based on the second ratio, one of the two candidate positions is determined as the target position; Based on the target position and the center position of the cross-section to be measured, the bending direction of the structure to be measured is determined to be from the center position of the cross-section to be measured toward the target position; The bending radius of the cross section to be measured is obtained based on the position of the third fiber grating sensor, the center position of the cross section to be measured, the bending direction, and the mode field offset of the third fiber grating sensor.

2. The sensing and monitoring method based on a single-core optical fiber according to claim 1, characterized in that, The method further includes: The target three-dimensional shape of the structure under test is determined based on the bending direction, the bending radius, and the pre-constructed initial three-dimensional shape of the structure under test.

3. The sensing and monitoring method based on a single-core optical fiber according to claim 1, characterized in that, The first fiber Bragg grating sensor, the second fiber Bragg grating sensor, and the third fiber Bragg grating sensor are arranged in an equilateral triangle on the cross section to be measured, and the distances from the first position, the second position, and the third position to the axis of the fiber core are equal. Furthermore, the first fiber Bragg grating sensor, the second fiber Bragg grating sensor, and the third fiber Bragg grating sensor are all disposed at the boundary between the fiber core and the cladding.

4. The single-core optical fiber according to claim 1, characterized in that, The plurality of fiber Bragg grating sensors are evenly distributed in the fiber core.

5. The single-core optical fiber according to claim 4, characterized in that, The single-core optical fiber is attached to the structure under test, and the bending direction of the plurality of fiber Bragg grating sensors follows the bending direction of the structure under test. The distance between adjacent fiber Bragg grating sensors on the cross section to be measured is consistent.

6. The single-core optical fiber according to claim 1, characterized in that, Each fiber Bragg grating sensor is fabricated point by point using a femtosecond laser.

7. The single-core optical fiber according to claim 1, characterized in that, The center wavelengths of the plurality of fiber optic grating sensors are separated by at least 2 nanometers.

8. A sensing and monitoring system based on a single-core optical fiber, characterized in that, Includes a single-core optical fiber, which is attached to the structure under test; The single-core optical fiber includes: a fiber core for transmitting optical signals; a cross-section to be measured pre-set on the fiber core; and multiple fiber Bragg grating sensors, circumferentially distributed in the fiber core, each fiber Bragg grating sensor being parallel to the axis of the fiber core; each of the multiple fiber Bragg grating sensors has a different center wavelength; wherein, the multiple fiber Bragg grating sensors include a first fiber Bragg grating sensor, a second fiber Bragg grating sensor, and a third fiber Bragg grating sensor; The first fiber optic sensor is located at the first position of the cross section to be measured; The second fiber optic sensor is located at a second position on the cross section to be measured; The third fiber optic grating sensor is located at the third position of the cross section to be measured; Each fiber Bragg grating sensor is parallel to the normal to the cross section to be measured; the system includes: The receiving module is used to control one end of the single-core optical fiber to receive the working light source; The acquisition module is used to acquire the light intensity reflected by each fiber Bragg grating sensor from the working light source, acquire the strain-reflected light intensity peak of the reflected light output by each fiber Bragg grating sensor on its measured cross section under strain, and acquire the initial reflected light intensity peak of each fiber Bragg grating sensor on its measured cross section when the fiber Bragg grating sensor is in its initial state; and The determination module is used for: The mode field offset of each fiber optic grating sensor is obtained by comparing the peak value of strain reflected light intensity with the peak value of initial reflected light intensity. Obtain a first ratio of the peak strain-reflected light intensity of the first fiber Bragg grating sensor to the peak initial reflected light intensity, and a second ratio of the peak strain-reflected light intensity of the second fiber Bragg grating sensor to the peak initial reflected light intensity. Based on the first ratio, two candidate positions are determined on the cross-section to be measured; Based on the second ratio, one of the two candidate positions is determined as the target position; Based on the target position and the center position of the cross-section to be measured, the bending direction of the structure under test is determined to be from the center position of the cross-section to be measured toward the target position; and The bending radius of the cross section to be measured is obtained based on the position of the third fiber grating sensor, the center position of the cross section to be measured, the bending direction, and the mode field offset of the third fiber grating sensor.

9. A bending measuring device, characterized in that, include: A laser is used to output a working light source; A single-core optical fiber, the single-core optical fiber comprising a fiber core and a plurality of fiber grating sensors located on the fiber core; The single-core optical fiber is used to: receive the working light source and output the light intensity reflected from the working light source through each fiber Bragg grating sensor; and The single-core optical fiber includes: a fiber core for transmitting optical signals; a cross-section to be measured pre-set on the fiber core; and multiple fiber Bragg grating sensors, circumferentially distributed in the fiber core, each fiber Bragg grating sensor being parallel to the axis of the fiber core; each of the multiple fiber Bragg grating sensors has a different center wavelength; wherein, the multiple fiber Bragg grating sensors include a first fiber Bragg grating sensor, a second fiber Bragg grating sensor, and a third fiber Bragg grating sensor; The first fiber optic sensor is located at the first position of the cross section to be measured; The second fiber optic sensor is located at a second position on the cross section to be measured; The third fiber optic grating sensor is located at the third position of the cross section to be measured; The controller, connected to the single-core optical fiber, is used for: Obtain the peak value of the strain-reflected light intensity of the reflected light output by each fiber Bragg grating sensor under strain conditions; Obtain the initial peak value of the reflected light intensity of the reflected light output by each fiber Bragg grating sensor when it is in its initial state; The mode field offset of each fiber optic grating sensor is obtained by comparing the peak value of strain reflected light intensity with the peak value of initial reflected light intensity. Obtain a first ratio of the peak strain-reflected light intensity of the first fiber Bragg grating sensor to the peak initial reflected light intensity, and a second ratio of the peak strain-reflected light intensity of the second fiber Bragg grating sensor to the peak initial reflected light intensity. Based on the first ratio, two candidate positions are determined on the cross-section to be measured; Based on the second ratio, one of the two candidate positions is determined as the target position; Based on the target location and the center location of the cross-section to be measured, the bending direction of the structure to be measured is determined; and The bending radius of the cross section to be measured is obtained based on the position of the third fiber grating sensor, the center position of the cross section to be measured, the bending direction, and the mode field offset of the third fiber grating sensor.

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