Multimode optical fiber mechanical sensing system and method based on wavefront shaping technology

Abstract

The invention relates to the technical field of mechanical sensing, and provides a multimode optical fiber mechanical sensing system and method based on a wavefront shaping technology, and the system employs the wavefront shaping technology to form a first focus point image at the far end of a step refractive index optical fiber. The stress condition of the step refractive index optical fiber is determined by analyzing the first focus point image, and finally the mechanical sensing system which is high in sensitivity, wide in range and free of limitation is obtained. The system comprises a light splitting unit, a signal light processing unit, a combined light beam unit, a camera and a main processing unit, wherein the main processing unit is used for performing singular value decomposition on a first focus point image to obtain a plurality of first singular values; extracting a first left singular vector corresponding to the maximum first singular value; calculating a first deviation value of the first left singular vector and a preset initial vector; and inputting the first deviation value into a preset external force change fitting curve formula to output a stress value, and determining the stress value as the current stress value of the step refractive index optical fiber.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of mechanical sensing, and in particular to a multimode fiber mechanical sensing system and method based on wavefront shaping technology. BACKGROUND

[0002] Multimode fiber (MMF) has been widely used in the field of sensing. Unlike single-mode fiber, the mode mixing and modal dispersion of light field transmission in multimode fiber, although it has been regarded as a thorny obstacle in the field of optical communication and optical imaging, can help sensing.

[0003] In the related art, many multimode interference (MMI) based sensing systems support the measurement of multiple parameters, such as temperature, contact force, bending, refractive index and displacement. Although these MMF based sensing systems have different structures, in terms of analysis objects, they can be divided into two categories: speckle analysis and spectral analysis. The former mainly relies on speckle correlation analysis and deep learning algorithms, while the latter relies on the drift of peak values or critical wavelengths in the transmission spectrum. However, the spectral analysis method usually has a relatively complex experimental system and more stringent detection means, and the speckle analysis method has certain limitations. SUMMARY

[0004] Therefore, the present application provides a multimode fiber mechanical sensing system and method based on wavefront shaping technology. In the system, a first focal point image is formed at the distal end of a step-index fiber using wavefront shaping technology, and the stress condition of the step-index fiber is determined by analyzing the first focal point image, so that a high-sensitivity, large-range and non-limited mechanical sensing system is finally obtained.

[0005] According to an aspect of the present application, a multimode fiber mechanical sensing system based on wavefront shaping technology is provided, comprising a light splitting unit, a signal light processing unit, a reference light processing unit, a merged light beam unit, a camera and a main processing unit; wherein the light splitting unit is used to generate signal light and reference light; the signal light is input to the signal light processing unit, and the reference light is input to the reference light processing unit; The signal light processing unit comprises, in sequence, a light shaping unit, a coupling optimization unit, a step-index fiber and a collimating unit; The merged light beam unit is used to merge and process the processed reference light output by the reference light processing unit and the processed signal light output by the signal light processing unit; The camera is used to generate a first focal point image based on the first merged and processed light beam output by the merged light beam unit under an actual measurement scene after the step-index fiber is stressed; The main processing unit is configured to receive the first focus point image generated by the camera, perform singular value decomposition on the first focus point image to obtain a plurality of first singular values, extract a first left singular vector corresponding to a largest first singular value, calculate a first deviation value of the first left singular vector and a preset initial vector, input the first deviation value into a preset external force change fitting curve formula to output a stress value, and determine the stress value as a current stress value of the step-index fiber; wherein the preset initial vector and the preset external force change fitting curve formula are determined based on second focus point images generated by the camera when no force and different forces are applied to the step-index fiber in an experimental test scenario.

[0006] In some embodiments, the light splitting unit includes a laser, an isolator, a first lens, a first mirror, a second lens, a second mirror, a first half-wave plate, a third lens, and a light splitter. The light beam output by the laser enters the isolator, the first lens expands the light beam output by the isolator, the first mirror adjusts the coupling position and direction of the light beam output by the first lens, the second lens expands the light beam output by the first mirror, the second mirror adjusts the coupling position and direction of the light beam output by the second lens, the light beam output by the second mirror enters the first half-wave plate, the third lens expands the light beam output by the first half-wave plate, and the light splitter splits the light beam output by the third lens into signal light and reference light.

[0007] In some embodiments, the light shaping unit includes a first variable optical attenuator, a first polarization maintaining optical fiber, a fourth lens, and a second half-wave plate. The signal light enters the first variable optical attenuator, the light beam output by the first variable optical attenuator enters the first polarization maintaining optical fiber, the fourth lens collimates the light beam output by the first polarization maintaining optical fiber, and the light beam output by the fourth lens is irradiated to the coupling optimization unit after passing through the second half-wave plate for polarization state control.

[0008] In some embodiments, the coupling optimization unit includes a spatial light modulator, a first polarizer, a third half-wave plate, a fifth lens, a beam shifter, a sixth lens, a seventh lens, a quarter-wave plate, and a first microscope objective. The spatial light modulator receives the light beam after polarization state control by the second half-wave plate; the first polarizer filters the light beam output by the spatial light modulator; the third half-wave plate controls the polarization state of the light beam output by the first polarizer; the light beam output by the third half-wave plate passes through the fifth lens, the beam shifter, the sixth lens, the seventh lens, the quarter-wave plate and the first microscope objective in sequence, and the light beam output by the first microscope objective enters the step-index fiber.

[0009] In some embodiments, the collimation unit comprises a second microscope objective and an eighth lens; The light beam output by the step-index fiber enters the second microscope objective, and the light beam output by the second microscope objective enters the combined beam unit through the eighth lens.

[0010] In some embodiments, the reference light processing unit comprises a second variable optical attenuator, a second polarization maintaining optical fiber, a ninth lens and a fourth half-wave plate; The reference light enters the second variable optical attenuator; the light beam output by the second variable optical attenuator enters the second polarization maintaining optical fiber, the ninth lens collimates the light beam output by the second polarization maintaining optical fiber; and the light beam output by the ninth lens enters the combined beam unit after passing through the fourth half-wave plate.

[0011] In some embodiments, the combined beam unit comprises a beam combiner and a tenth lens; The light beam output by the ninth lens and the light beam output by the fourth half-wave plate both enter the beam combiner to be combined to obtain a combined beam; and the combined beam enters the tenth lens and then enters the camera.

[0012] According to another aspect of the present application, a multi-mode fiber mechanical sensing method based on wavefront shaping technology is provided, which is applied to a main processing unit in the system, and the method comprises: receiving a first focus point image generated by the camera; processing the first focus point image to obtain a first left singular vector; calculating a first deviation value of the first left singular vector and a preset initial vector; inputting the first deviation value into a preset external force change fitting curve formula to output a stress value, and determining the stress value as a current stress value of the step-index fiber; wherein the preset initial vector and the preset external force change fitting curve formula are determined based on second focus point images generated by the camera when no force and different forces are applied to the step-index fiber in an experimental test scenario.

[0013] In some embodiments, the method further comprises determining a preset initial vector and a preset external force change fitting curve formula; wherein the step of determining the preset initial vector and the preset external force change fitting curve formula comprises: In an experimental test scenario, a plurality of second singular values are obtained by singular value decomposition of second focus point images generated by the camera when no force is applied to the step-index fiber and different forces are applied to the step-index fiber; a second left singular vector corresponding to a maximum second singular value is extracted, and the second left singular vector determined when no force is applied to the step-index fiber is determined as a preset initial vector; Second deviation values of the second left singular vectors determined when different forces are applied to the step-index fiber and the preset initial vector are calculated; A preset external force change fitting curve formula is obtained by linear fitting of the corresponding second deviation values when different forces are applied.

[0014] In some embodiments, before the camera generates the second focus point image, the method further comprises: receiving a third focus point image generated by the camera; using a second combined processed light beam used to generate the third focus point image as input data, and using the third focus point image as output data; constructing a transmission matrix of the step-index fiber based on the input data and the output data; controlling the spatial light modulator based on the transmission matrix, so that the third focus point image has a focus point.

[0015] According to another aspect of the present application, a computer device is provided, which comprises a storage medium, a processor, and a computer program stored in the storage medium and executable on the processor, wherein the processor executes the multi-mode fiber mechanical sensing method based on the wavefront shaping technology.

[0016] According to another aspect of the present application, a storage medium is provided, which stores a computer program, wherein the program is executed by a processor to implement the multi-mode fiber mechanical sensing based on the wavefront shaping technology.

[0017] By means of the above technical solutions, the present application provides a multi-mode fiber mechanical sensing system and method based on the wavefront shaping technology. In the system, the wavefront shaping technology is used to form a first focus point image at a distal end of a step-index fiber, and the force on the step-index fiber is determined by analyzing the first focus point image, so that a high-sensitivity, large-range, and non-limited mechanical sensing system is ultimately obtained.

[0018] The above description is only a summary of the technical solutions of the present application. In order to enable the technical means of the present application to be more clearly understood, and to be implemented according to the content of the description, and in order to enable the above and other purposes, characteristics and advantages of the present application to be more apparent and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0019] The drawings described herein are used to provide further understanding of the present application, and form a part of the present application. The schematic embodiments of the present application and the description thereof are used to explain the present application, and do not constitute an improper limitation on the present application. In the drawings: Figure 1 An exemplary structural schematic diagram of a multi-mode optical fiber mechanical sensing system based on wavefront shaping technology is shown; Figure 2 The contribution distribution curve of the first 10 principal components of the focal point image in the initial state; Figures 3-10 The contribution distribution curve of the first 10 principal components of different speckles obtained at different coupling angles in the initial state; Figures 11-12 An exemplary schematic diagram of different preset external force change fitting curves provided according to some embodiments is shown; Figure 13 The focal point images corresponding to different forces on the optical fiber are shown; Figure 14 An exemplary flowchart of a multi-mode optical fiber mechanical sensing method based on wavefront shaping technology is shown.

[0020] Wherein, 1-laser; 2-isolator; 3-first lens; 4-first mirror; 5-second lens; 6-second mirror; 7-first half-wave plate; 8-third lens; 9-beamsplitter; 10-first variable optical attenuator; 11-first polarization maintaining optical fiber; 12-fourth lens; 13-second half-wave plate; 14-space light modulator; 15-first polarizer; 16-third half-wave plate; 17-fifth lens; 18-beam displacer; 19-sixth lens; 20-seventh lens; 21-quarter-wave plate; 22-first microscope objective; 23-step-index fiber; 24-weight; 25-second variable optical attenuator; 26-second polarization maintaining optical fiber; 27-ninth lens; 28-fourth half-wave plate; 29-second microscope objective; 30-eighth lens; 31-beam combiner; 32-tenth lens; 33-camera. DETAILED DESCRIPTION

[0021] The present application will be described in detail below with reference to the drawings and in conjunction with embodiments. It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0022] In the related art, many MMI-based sensing systems support the measurement of multiple parameters, such as temperature, contact force, bending, refractive index, and displacement. Although these MMF-based sensing systems have different structures, in terms of the analysis object, they can be divided into two categories: speckle analysis and spectral analysis. The former mainly relies on speckle correlation analysis and deep learning algorithms, while the latter relies on the shift of the peak or critical wavelength in the transmission spectrum. However, the spectral analysis method usually has a relatively complex experimental system and more stringent detection means, and the speckle analysis method has certain limitations.

[0023] Specifically, the spectral analysis method relies on detecting the shift of the peak or critical wavelength in the transmission spectrum when the external parameter changes. A high-sensitivity surface plasmon resonance (SPR) sensor based on a multi-mode fiber (MMF)-tapered hollow-core fiber (THCF)-MMF structure in the related art is used for refractive index (RI) sensing, and a new sensing method is proposed: as the RI increases, the MMI peak will have a blue shift, which is opposite to the direction of the SPR peak. By monitoring the difference between the two resonance peaks, a high-sensitivity RI sensor can be obtained. For a MMF-THCF-MMF probe with a normal hollow-core fiber (HCF) core diameter of 30 μm and a taper ratio of 3.3, by monitoring the wavelength difference, the sensitivity at RI of 1.40 can reach 7592.25 nm / RIU, which is higher than the sensitivity of monitoring only the SPR peak. However, this type of spectral analysis method usually has a relatively complex experimental system and more stringent detection means.

[0024] Speckle analysis mainly relies on correlation analysis of speckle patterns or deep learning algorithms. When the light field is transmitted in the multi-mode fiber, it is affected by mode dispersion and modal mixing, and changes occur, thus forming random distribution irregular speckles at the far end of the fiber. These speckle images contain a variety of modes and are very sensitive to changes in the external environment. By analyzing the changes in these speckles, a variety of physical parameters can be measured. In a related technology, a single MMF structure is used, and the intensity and modal phase deviation are quantified to analyze the normalized intensity product (NIPC) of the fiber speckle pattern, and the size or position of the force applied on a 30x30 square millimeter array is measured. Although this system responds reliably to a single point excitation, it still needs to use other technologies to evaluate the size and position of multiple forces; another related technology proposes a new structure of ultra-short multi-mode optical fiber for fiber speckle sensing, and demonstrates its application in multi-bending sensing. This speckle pattern analysis-based sensing method has the advantages of simple system, low cost and high sensitivity, but the limitations of the speckle pattern sensor are mainly related to the use of a digital camera to capture the speckle pattern for analysis. Generally speaking, the larger the field of view (FOV), the more speckle information can be counted. However, this conflicts with the requirement that every speckle in the field of view should be digitally resolved, especially when the camera bandwidth and data transmission are limited.

[0025] To solve the above technical problems, the embodiments of the present application propose a multi-mode optical fiber mechanical sensing system and method based on wavefront shaping technology. In the system, wavefront shaping technology is used to form a first focused point image at the far end of the step-index optical fiber. By analyzing the first focused point image, the stress condition of the step-index optical fiber is determined, and finally a high-sensitivity, large-range, and non-limited mechanical sensing system is obtained.

[0026] The wavefront shaping (WFS) technology mentioned in the embodiments of the present application is used to compensate for optical scattering to achieve depth-limited diffraction optical focusing in complex media. In the embodiments of the present application, the changes of the main characteristics of the focused point are analyzed to track the changes of the physical environment of the optical fiber.

[0027] Specifically, the embodiments of the present application provide a multi-mode optical fiber mechanical sensing system based on wavefront shaping technology. The system comprises a light splitting unit, a signal light processing unit, a reference light processing unit, a combined beam unit, a camera and a main processing unit.

[0028] The light splitting unit is used to generate signal light and reference light; the signal light is input to the signal light processing unit, and the reference light is input to the reference light processing unit.

[0029] In some embodiments, Figure 1An exemplary structure diagram of a multi-mode fiber mechanical sensing system based on wavefront shaping technology is shown. The light splitting unit includes a laser 1, an isolator 2, a first lens 3, a first mirror 4, a second lens 5, a second mirror 6, a first half-wave plate 7, a third lens 8, and a light splitter 9.

[0030] The laser 1 outputs a light beam into the isolator 2.

[0031] In the embodiment, the laser 1 is configured to provide a light source for the system. The isolator 2 can prevent reflected light in the system from returning to the laser 1.

[0032] The first lens 3 expands the light beam output by the isolator 2. The first mirror 4 adjusts the coupling position and direction of the light beam output by the first lens 3. The second lens 5 expands the light beam output by the first mirror 4. The second mirror 6 adjusts the coupling position and direction of the light beam output by the second lens 5. The second mirror 6 outputs a light beam into the first half-wave plate 7.

[0033] In the embodiment, the first half-wave plate 7 can adjust the splitting ratio of the light beam coupled into the light splitter 9.

[0034] The third lens 8 expands the light beam output by the first half-wave plate 7. The light beam output by the third lens 8 is transmitted into the light splitter 9, which splits the light beam output by the third lens 8 into signal light and reference light. In one example, the splitting ratio of the signal light is 98%, and the splitting ratio of the reference light is 2%.

[0035] The signal light processing unit includes, in sequence, a light shaping unit, a coupling optimization unit, a step-index fiber, and a collimation unit.

[0036] In some embodiments, the light shaping unit includes a first variable optical attenuator 10, a first polarization maintaining fiber 11, a fourth lens 12, and a second half-wave plate 13. The signal light is transmitted into the first variable optical attenuator 10. In the embodiment, the first variable optical attenuator 10 can control the intensity of the signal light.

[0037] The light beam output by the first variable optical attenuator 10 is transmitted into the first polarization maintaining fiber 11. The fourth lens 12 collimates the light beam output by the first polarization maintaining fiber 11. The light beam output by the fourth lens 12 is irradiated to the coupling optimization unit after polarization state control by the second half-wave plate 13.

[0038] In the embodiment, the light beam output by the second half-wave plate is irradiated to the spatial light modulator 14 in the coupling optimization unit.

[0039] In some embodiments, the coupling optimization unit comprises a spatial light modulator 14, a first polarizer 15, a third half-wave plate 16, a fifth lens 17, a beam shifter 18, a sixth lens 19, a seventh lens 20, a quarter-wave plate 21, and a first microscope objective 22. The spatial light modulator 14 receives the light beam after the polarization state control by the second half-wave plate 13; the first polarizer 15 filters the light beam output by the spatial light modulator 14; the third half-wave plate 16 controls the polarization state of the light beam output by the first polarizer 15; and the light beam output by the third half-wave plate 16 passes through the fifth lens 17, the beam shifter 18, the sixth lens 19, the seventh lens 20, the quarter-wave plate 21, and the first microscope objective 22 in sequence.

[0040] In the embodiments of the present application, the light beam passes through the fifth lens 17, the beam shifter 18, the sixth lens 19, the seventh lens 20, and the quarter-wave plate 21 in sequence to change the polarization state.

[0041] The light beam output by the first microscope objective is transmitted into the step-index fiber. The step-index fiber in the embodiments of the present application is a multimode fiber.

[0042] In some embodiments, the collimation unit comprises a second microscope objective 29 and an eighth lens 30.

[0043] The light beam output by the step-index fiber is transmitted into the second microscope objective 29, and the light beam output by the second microscope objective 29 is transmitted into the merging beam unit through the eighth lens 30.

[0044] In the embodiments of the present application, the light beam output by the step-index fiber is transmitted into the beam combiner 31 in the merging beam unit after being expanded by the second microscope objective 29 and the eighth lens 30.

[0045] In some embodiments, the reference light processing unit comprises a second variable optical attenuator 25, a second polarization-maintaining fiber 26, a ninth lens 27, and a fourth half-wave plate 28. The reference light is transmitted into the second variable optical attenuator 25. In the embodiments of the present application, the second variable optical attenuator 25 can control the intensity of the reference light. The light beam output by the second variable optical attenuator 25 is transmitted into the second polarization-maintaining fiber 26, the light beam output by the second polarization-maintaining fiber 26 is collimated by the ninth lens 27, and the light beam output by the ninth lens 27 is input into the merging beam unit through the fourth half-wave plate 28.

[0046] In the embodiments of the present application, the light beam output by the fourth half-wave plate 28 is input into the beam combiner 31 in the merging beam unit.

[0047] The combined light beam unit is configured to combine the processed reference light output by the reference light processing unit and the processed signal light output by the signal light processing unit.

[0048] In some embodiments, the combined light beam unit comprises a beam combiner 31 and a tenth lens 32.

[0049] The light beam output by the ninth lens 27 and the light beam output by the fourth half-wave plate 28 are both transmitted into the beam combiner 31 and combined to obtain a combined light beam, which is transmitted into the tenth lens 32 and the camera 33.

[0050] The camera 33 is configured to generate a first focal point image based on the first combined processed light beam output by the combined light beam unit when the step-index fiber 23 is stressed in an actual measurement scene.

[0051] In the embodiments, the camera generates a first focal point image based on the first combined processed light beam output by the combined light beam unit when the step-index fiber is stressed in an actual measurement scene. Specifically, the tenth lens in the combined light beam unit outputs the first combined processed light beam after receiving the combined light beam, and the camera generates the first focal point image after receiving the first combined processed light beam.

[0052] In one example, the actual measurement scene can be measuring the gravity of an object, and the step-index fiber is stressed by placing the object on the step-index fiber. The stress value output by the main processing unit is the gravity of the object.

[0053] The main processing unit is configured to receive the first focal point image generated by the camera, perform singular value decomposition (SVD) on the first focal point image to obtain a plurality of first singular values, extract a first left singular vector corresponding to the maximum first singular value, calculate a first deviation value of the first left singular vector and a preset initial vector, input the first deviation value into a preset external force change fitting curve formula to output a stress value, and determine the stress value as the current stress value of the step-index fiber. The preset initial vector and the preset external force change fitting curve formula are determined based on second focal point images generated by the camera when the step-index fiber is not stressed and stressed by different forces in an experimental test scene.

[0054] In the embodiments, the first left singular vector corresponding to the maximum first singular value in the first focal point image is extracted by singular value decomposition. Specifically, the first left singular vector can be extracted according to the following formulas (1)-(3): (1) (2) (3) wherein, is denoted as a first focus point image; U, and V are respectively a left singular vector matrix, a singular value matrix and a right singular vector matrix obtained by singular value decomposition on the first focus point image, the singular value matrix comprising a plurality of first singular values, the left singular vector matrix comprising a plurality of first left singular vectors corresponding to the first singular values; is a first singular value, and the eigenvalue has a quadratic relationship; is a first singular value is a first left singular vector corresponding to the first singular value, and r = min(a, b), where a represents a number of horizontal pixel points in the first focus point image, and b represents a number of vertical pixel points in the first focus point image.

[0055] The first singular value reflects how the energy or information quantity in the first focus point image is distributed in different directions. The largest first singular value indicates that the corresponding direction contains more information or changes (i.e., higher energy), and its corresponding eigenvalue is often associated with the main feature or mode of the first focus point image and can best reflect the influence of external factors on the focus point.

[0056] In some embodiments, the method further comprises determining a preset initial vector and a preset external force change fitting curve formula; wherein the step of determining the preset initial vector and the preset external force change fitting curve formula comprises: under an experimental test scene, performing singular value decomposition on the second focus point images generated by the camera when no force and different forces are applied on the step-index fiber to obtain a plurality of second singular values; extracting a second left singular vector corresponding to the largest second singular value, and determining the second left singular vector determined when no force is applied on the step-index fiber as the preset initial vector; calculating second deviation values of the second left singular vectors determined when different forces are applied on the step-index fiber from the preset initial vector respectively; and performing linear fitting on the corresponding second deviation values when different forces are applied to obtain the preset external force change fitting curve formula.

[0057] In one example, different forces can be achieved by placing different weights of weights 24 on the step-index fiber. In another example, different forces can be achieved by using a press machine on the step-index fiber.

[0058] ​In the embodiment of the present application, before testing the stress condition of the step-index fiber in the actual test scene, a second focal point image is generated in an experimental test scene. The process of generating the second focal point image is the same as that of generating the first focal point image in the actual test scene, that is, first, a laser is used to emit a light beam, and then a focal point image is generated by using the structure in the system. Subsequently, the preset initial vector and the preset external force change fitting curve formula are determined by using the second focal point image generated in the experimental test scene.

[0059] In the embodiment of the present application, the SVD processing is performed on each second focal point image under different stress conditions, and the second left singular vector corresponding to the maximum second singular value representing the main feature of the second focal point image is extracted as an important parameter reflecting the physical state change of the fiber. In the embodiment, the formula used for calculating the second left singular vector from the second focal point image is the same as that used for calculating the first left singular vector from the first focal point image mentioned above. The second left singular vector determined when no force is applied to the step-index fiber is determined as the preset initial vector.

[0060] In the embodiment of the present application, the second deviation value of the second left singular vector determined when different forces are applied to the step-index fiber and the preset initial vector is calculated. Specifically, the second deviation value between the second left singular vector and the preset initial vector can be calculated by using the Euclidean distance method, and the second deviation value can be calculated by using formula (4): (4) wherein, is the i th element in the preset initial vector, is the i th element in the second left singular vector of the second focal point image under different stress conditions. The value of D increases with the increase of the difference between the second left singular vector and the preset initial vector. n is the length of the second left singular vector, that is, the total number of elements contained in the second left singular vector.

[0061] In the embodiment of the present application, the second deviation values corresponding to different forces are linearly fitted to obtain the preset external force change fitting curve formula. The linear fitting method can be MATLAB linear fitting. The abscissa of the preset external force change fitting curve can be the external force, and the ordinate can be the second deviation value.

[0062] In the embodiment of the present application, a focal point is formed at the distal end of the step-index fiber by wavefront shaping technology, and a preset external force change fitting curve formula is established by analyzing the change of the focal point image under the stress condition of the step-index fiber.

[0063] The preset initial vector and the preset external force change fitting curve formula can be determined through the above steps.

[0064] In the embodiments of the present application, the first deviation value of the first left singular vector and the preset initial vector can be calculated in the same way as the second deviation value of the second left singular vector and the preset initial vector. Since the above has been described in detail, it will not be repeated here.

[0065] In the embodiments of the present application, the first deviation value can be input into the preset external force change fitting formula, and then the corresponding stress value is obtained, which is taken as the current stress value of the step-index fiber. If the scenario of placing an object on the step-index fiber, the current stress value calculated is the gravity of the object.

[0066] In some embodiments, before the camera generates a second focus point image, it further includes: receiving a third focus point image generated by the camera; taking the second merged processed light beam used to generate the third focus point image as input data, and taking the third focus point image as output data; based on the input data and the output data, constructing a transmission matrix of the step-index fiber; based on the transmission matrix, regulating the spatial light modulator to make the third focus point image have a focus point.

[0067] In the embodiments of the present application, the process of generating the third focus point image and the first focus point image is the same, which is first using a laser to emit a light beam, and then using the structure in the system to generate a focus point image.

[0068] In the embodiments of the present application, the spatial light modulator can adjust the amplitude, phase and polarization state of the light beam entering the step-index fiber. Before determining the preset initial vector and the preset external force change fitting curve formula, the spatial light modulator needs to be regulated, specifically to establish the light field correspondence between the input and output of the step-index fiber, and based on this to construct the transmission matrix of the step-index fiber. The transmission matrix is used to accurately regulate the spatial light modulator to make the amplitude and phase of the output light of the step-index fiber, so as to generate obvious focus points at the output end of the step-index fiber.

[0069] In the embodiments of the present application, the transmission matrix of the step-index fiber is constructed based on the input data and the output data using the holographic interference projection method.

[0070] In the embodiments of the present application, the feasibility of the system in the embodiments of the present application is verified through experiments. Specifically, principal component analysis is used to analyze the feature distribution difference of the focused point image and the speckle image. Here, the principal component can be understood as the direction of capturing image information, and the higher the contribution rate of the principal component, the more information distributed along this direction. When a few principal components of an image have much higher contribution rate than other principal components, it indicates that most information of the image is concentrated in a few directions, otherwise, it indicates that the information of the image is relatively dispersed. In order to increase the completeness of the analysis, speckle images obtained at different coupling angles are also selected to compare with the focused point image. Figure 2 The contribution rate distribution curve of the first 10 principal components of the focused point image in the initial state (no force applied on the step index fiber). Figures 3-10 The contribution rate distribution curve of the first 10 principal components of different speckles obtained at different coupling angles in the initial state. It can be clearly seen from the figure that the maximum principal component contribution rate of the focused point image is as high as 0.99 or more, and the image information is mostly concentrated in the direction corresponding to the maximum principal component. The maximum principal component contribution rate of the speckle image is between 0.2 and 0.6, and the image information is relatively dispersed compared with the focused point image. Therefore, it can be concluded that the focused point image obtained by using the wavefront shaping technology has concentrated information and distinct features, and it is expected to obtain external information by tracking the feature change of the focused point image.

[0071] The technical effects of the method in the embodiments of the present application are shown in Figure 11 and 12 . Figure 11 The experimental results of the system are shown, and the force measurement range is from 0.5N to 5N. The blue line is the linear fitting curve of the second deviation value and the external force on the fiber, and the fitting R 2 is 0.9948, and the determined preset external force change fitting curve formula is y1=0.00567x+0.00120, where x is the external force and y is the second deviation value. Figure 12 The resolution capability of the system is further shown, and the minimum resolution is 0.05N, and the fitting R 2 is 0.977, and the determined preset external force change fitting curve formula is y1=0.00532x+0.00110, where x is the external force and y is the second deviation value. Figure 13 are the corresponding focused point images under different forces on the fiber, and all the images have been logarithmically processed and normalized. It can be seen that as the external force on the fiber increases, the noise around the focused point increases, but the center still shows a bright dot. The above results all show that based on the wavefront shaping technology, a large range and high sensitivity system is established in the embodiments of the present application.

[0072] By applying the technical solutions in the above-mentioned embodiments, a multimode fiber mechanical sensing system based on wavefront shaping technology is provided. In the system, a first focal point image is formed at the distal end of a step-index fiber by using wavefront shaping technology. The stress condition of the step-index fiber is determined by analyzing the first focal point image, and finally a mechanical sensing system with high sensitivity, large range and no limitation is obtained. The force measurement range is 0-0.5N, and the minimum resolution is 0.05N.

[0073] In some embodiments, as a specific implementation of the multimode fiber mechanical sensing system based on wavefront shaping technology described in the above-mentioned embodiments, the present application further provides a multimode fiber mechanical sensing method based on wavefront shaping technology, which is applied to the main processing unit in the system.

[0074] Figure 14 An exemplary flowchart of a multimode fiber mechanical sensing method based on wavefront shaping technology according to some embodiments is shown. The method includes S100-S300. S100, receiving a first focal point image generated by a camera; S200, processing the first focal point image to obtain a first left singular vector; calculating a first deviation value of the first left singular vector and a preset initial vector; S300, inputting the first deviation value into a preset external force change fitting curve formula to output a stress value, and determining the stress value as the current stress value of the step-index fiber; wherein the preset initial vector and the preset external force change fitting curve formula are determined based on second focal point images generated by the camera when no force and different forces are applied to the step-index fiber in an experimental test scenario.

[0075] It should be noted that the corresponding description of the steps involved in the multimode fiber mechanical sensing method based on wavefront shaping technology provided by the embodiments of the present application can refer to the corresponding description in the multimode fiber mechanical sensing system based on wavefront shaping technology provided by the above-mentioned embodiments, which will not be described here.

[0076] The embodiments of the present application also provide a computer device, which can be a personal computer, a server, a network device, etc. The computer device includes a bus, a processor, a memory and a communication interface, and can also include an input / output interface and a display device. The processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store location information. The network interface of the computer device is used to communicate with external terminals through network connection. The computer program is executed by the processor to implement the steps in the method embodiments.

[0077] Those skilled in the art can understand that the structure of the computer device described above is only part of the structure related to the scheme of the present application, and does not constitute a limitation on the computer device to which the scheme of the present application is applied. A specific computer device can include more or fewer components, or combine certain components, or have a different arrangement of components.

[0078] In an embodiment, a computer readable storage medium is also provided, which can be non-volatile or volatile, and has stored thereon a computer program which, when executed by a processor, implements the steps of any of the above method embodiments.

[0079] In an embodiment, a computer program product is also provided, comprising a computer program which, when executed by a processor, implements the steps of any of the above method embodiments.

[0080] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data for analysis, stored data, displayed data, etc.) involved in the present application are all information and data authorized by the user or authorized by all parties.

[0081] Those of ordinary skill in the art can understand that all or part of the processes in the above-mentioned embodiments can be completed by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer readable storage medium. When the computer program is executed, it can include the processes of the above-mentioned embodiments.

[0082] The technical features of the above embodiments can be combined in any way. To make the description concise, not all possible combinations of the technical features in the above embodiments are described, but as long as the combinations of the technical features do not exist contradictions, they should be considered as the scope of the present application.

[0083] The above-described embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the scope of the present application. Therefore, the scope of the present application should be subject to the appended claims.

Claims

1. A multimode optical fiber mechanical sensing system based on wavefront shaping technology, characterized in that: include: A spectroscopic unit, a signal light processing unit, a reference light processing unit, a beam combining unit, a camera, and a main processing unit; wherein the spectroscopic unit is configured to generate signal light and reference light; input the signal light into the signal light processing unit, and input the reference light into the reference light processing unit; A signal light processing unit, comprising a light shaping unit, a coupling optimization unit, a step-index optical fiber, and a collimation unit connected in sequence; a beam merging unit, configured to merge the processed reference light output by the reference light processing unit and the processed signal light output by the signal light processing unit; a camera, configured to generate a first focused point image based on the first combined processed light beam output by the light beam combining unit after a force is applied to the step-index optical fiber in an actual measurement scenario; A main processing unit is configured to receive a first focus point image generated by the camera; perform singular value decomposition on the first focus point image to obtain multiple first singular values; extract a first left singular vector corresponding to the largest first singular value; calculate a first deviation value between the first left singular vector and a preset initial vector; input the first deviation value into a preset external force change fitting curve formula to output a force value, and determine the force value as the current force value of the step-index optical fiber; wherein the preset initial vector and the preset external force change fitting curve formula are determined in an experimental test scenario based on a second focus point image generated by the camera when no force is applied to the step-index optical fiber and when different forces are applied.

2. The system according to claim 1, wherein: The light splitting unit includes a laser, an isolator, a first lens, a first reflector, a second lens, a second reflector, a first half-wave plate, a third lens and a light splitter; The light beam output by the laser is transmitted into the isolator; the first lens expands the light beam output by the isolator; the first reflector adjusts the coupling position and direction of the light beam output by the first lens; the second lens expands the light beam output by the first reflector; the second reflector adjusts the coupling position and direction of the light beam output by the second lens; the light beam output by the second reflector is transmitted into the first half-wave plate; the third lens expands the light beam output by the first half-wave plate; the light beam output by the third lens is transmitted into the spectrometer, and the spectrometer splits the light beam output by the third lens into signal light and reference light.

3. The system according to claim 1, wherein: The light shaping unit includes a first variable optical attenuator, a first polarization-maintaining optical fiber, a fourth lens and a second half-wave plate; The signal light is transmitted into the first variable optical attenuator; the light beam output by the first variable optical attenuator is transmitted into the first polarization-maintaining optical fiber; the fourth lens collimates the light beam output by the first polarization-maintaining optical fiber; the light beam output by the fourth lens is polarization-controlled by the second half-wave plate and then irradiated onto the coupling optimization unit.

4. The system according to claim 3, characterized in that The coupling optimization unit includes a spatial light modulator, a first polarizer, a third half-wave plate, a fifth lens, a beam shifter, a sixth lens, a seventh lens, a quarter-wave plate, and a first microscope objective lens; The spatial light modulator receives the light beam after the polarization state is controlled by the second half-wave plate; the first polarizer filters the light beam output by the spatial light modulator; the third half-wave plate controls the polarization state of the light beam output by the first polarizer; the light beam output by the third half-wave plate passes through the fifth lens, the beam shifter, the sixth lens, the seventh lens, the quarter-wave plate and the first microscope objective lens in sequence, and the light beam output by the first microscope objective lens is transmitted into the step-index optical fiber.

5. The system according to claim 4, characterized in that The collimating unit includes a second microscope objective lens and an eighth lens; The light beam outputted by the step-refractive-index optical fiber is transmitted to the second microscope objective lens, and the light beam outputted by the second microscope objective lens is transmitted to the beam combining unit through the eighth lens.

6. The system according to claim 5, characterized in that The reference light processing unit includes a second variable optical attenuator, a second polarization-maintaining optical fiber, a ninth lens, and a fourth half-wave plate; The reference light is transmitted into the second variable optical attenuator; the light beam output by the second variable optical attenuator is transmitted into the second polarization-maintaining fiber; the ninth lens collimates the light beam output by the second polarization-maintaining fiber; and the light beam output by the ninth lens passes through the fourth half-wave plate and is input into the beam combining unit.

7. The system according to claim 6, characterized in that The beam combining unit includes a beam combiner and a tenth lens; The light beam output by the ninth lens and the light beam output by the fourth half-wave plate are both input into the beam combiner to be combined to obtain a combined light beam; the combined light beam is input into the tenth lens and then into the camera.

8. A multimode optical fiber mechanical sensing method based on wavefront shaping technology, applied to the main processing unit of the system according to any one of claims 1 to 7, characterized in that: The method comprises: receiving a first focused point image generated by a camera; The first focus point image is processed to obtain a first left singular vector; a first deviation value between the first left singular vector and a preset initial vector is calculated; the first deviation value is input into a preset external force change fitting curve formula to output a force value, and the force value is determined as the current force value of the step-index optical fiber; wherein the preset initial vector and the preset external force change fitting curve formula are determined in an experimental test scenario based on the second focus point image generated by the camera when no force is applied to the step-index optical fiber and when different forces are applied.

9. The method according to claim 8, characterized in that The method further includes determining a preset initial vector and a preset external force change fitting curve formula; wherein the step of determining the preset initial vector and the preset external force change fitting curve formula includes: In an experimental test scenario, singular value decomposition is performed on the second focus point image generated by the camera when no force is applied to the step-index optical fiber and when different forces are applied, respectively, to obtain multiple second singular values; a second left singular vector corresponding to the largest second singular value is extracted, and the second left singular vector determined when no force is applied to the step-index optical fiber is determined as a preset initial vector; Calculating second deviation values ​​of the second left singular vector determined when different forces are applied to the step-index optical fiber and the preset initial vector; A linear fit is performed on the second deviation values ​​corresponding to different forces applied to obtain a preset external force change fitting curve formula.

10. The method according to claim 9, characterized in that Before the camera generates the second focused point image, the method further includes: receiving a third focus point image generated by the camera; using the second combined light beam for generating the third focused point image as input data and the third focused point image as output data; constructing a transmission matrix of a step-index optical fiber based on the input data and the output data; The spatial light modulator is controlled based on the transmission matrix so that the third focused point image has a focused point.

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