Square optical fiber curvature sensor and knee joint angle monitoring system

Abstract

The invention discloses a square optical fiber curvature sensor and a knee joint angle monitoring system, and relates to the technical field of optical fiber sensing. The square optical fiber is used for replacing a traditional optical fiber with a circular cross section, and a square optical fiber light field is distributed in a rectangular shape, so that when a rectangular light spot is subjected to mode excitation, due to uniform energy of the rectangular light spot, a large amount of light on two sides of the light spot can be excited to a high-order mode to form interference, and the sensitivity of the sensor is improved; in addition, the square optical fiber is provided with an etching cavity to form a Fabry-Perot resonant cavity, so that the sensitivity of the sensor is further improved.

Description

Technical Field

[0001] The present application relates to the field of optical fiber sensing technology, and in particular to a square optical fiber curvature sensor and a knee joint angle monitoring system. Background Art

[0002] Long-term monitoring of human motion and posture is an effective tool for diagnosing chronic diseases associated with brain degeneration, such as Parkinson's disease and stroke. Measuring knee joint motion is one of the most important health assessments in human motion and posture monitoring. By detecting and extracting data on knee flexion and bending during movement, doctors can assess a patient's disease progression or rehabilitation outcomes, thereby developing personalized treatment plans. Furthermore, many other related medical treatments benefit from continuous monitoring of knee flexion during treatment and rehabilitation.

[0003] In human motion and posture monitoring, the usual method is to use electronic strain gauges to measure the bending morphology of human joints, but these sensors are easily interfered with by temperature and electromagnetic fields, which affects the reliability of the measurement. In addition, optical goniometers such as dynamic goniometers and photoelectric encoders are also used to obtain joint motion information, but these devices require high-precision mechanical support and generate noise during operation. Inertial measurement units can also be used to measure knee bending, but they require frequent calibration and are highly sensitive to electromagnetic fields. These factors hinder the application of inertial measurement devices in practical applications. The development of miniaturized, more compatible, shorter response time and higher sensitivity sensors is the main research direction of knee joint detection sensors.

[0004] Due to their unique physical properties, optical fiber holds broad potential for application in biomechanical and medical sensing. Fiber optic sensors, due to the properties of glass fiber, offer advantages such as light weight and good biocompatibility. Furthermore, they offer excellent immunity to electromagnetic interference, high sensitivity, fast response time, and excellent safety. Furthermore, they are highly robust and low-cost. Therefore, fiber optic sensors offer a promising solution for highly secure and sensitive human motion detection.

[0005] Fiber-optic Mach-Zehnder sensors have been widely researched and applied due to their simple structure and high sensitivity. The interference effects generated by their structure can be caused by factors such as core diameter mismatch and multipath in microstructured optical fibers. To improve the sensitivity of fiber-optic Mach-Zehnder interferometers, the introduction of specialized optical fibers, such as multi-core, coreless, and multi-clad fibers, is an effective approach. However, the light field transmitted in existing optical fibers has a Gaussian shape. During mode excitation, this Gaussian light field distribution has relatively low energy on either side of the Gaussian curve, resulting in low energy in the higher-order modes excited. This results in weak excitation light energy and low sensor sensitivity. Summary of the Invention

[0006] The purpose of this application is to provide a square fiber optic curvature sensor and a knee joint angle monitoring system to improve the sensitivity of the fiber optic curvature sensor and thereby improve the sensitivity of knee joint angle monitoring.

[0007] To achieve the above objectives, this application provides the following solutions.

[0008] In a first aspect, the present application provides a square optical fiber curvature sensor, comprising: a first single-mode optical fiber, a square optical fiber, and a second single-mode optical fiber;

[0009] The first single-mode optical fiber is connected to one end of the square optical fiber, and the other end of the square optical fiber is connected to the second single-mode optical fiber;

[0010] The square optical fiber includes: a square fiber core and a cladding wrapping the square fiber core, wherein an etched cavity is etched on the cladding.

[0011] Optionally, the cladding includes a first cladding and a second cladding, wherein the first cladding is wrapped around the outside of the square core, and the second cladding is wrapped around the outside of the first cladding.

[0012] Optionally, the diameter of the square core is 50 μm, the diameter of the first cladding is 100 μm, and the diameter of the second cladding is 250 μm.

[0013] Optionally, the parameter information of the etched cavity is determined using the following formula:

[0014]

[0015] Where, I is the interference light intensity of the square fiber, I clad is the light intensity of the cladding mode of the square fiber, I core is the light intensity of the core mode of the square fiber, φ is the phase difference between the core mode and the cladding mode of the square fiber, I clad Related to the parameter information of the etched cavity, I cladThe relationship function with the parameter information of the etched cavity is obtained by establishing a relationship model through simulation data or experimental data.

[0016] Optionally, the length of the square optical fiber is determined using the following formula:

[0017]

[0018] Where FSR is the free spectral range, λ0 is the wavelength of the interference valley, Δn eff is the effective refractive index of the square fiber, and L is the interference length of the square fiber.

[0019] Optionally, the first single-mode optical fiber is connected to one end of the square optical fiber in the following manner:

[0020] Placing one end of the first single-mode optical fiber and one end of the square optical fiber on a fiber fusion splicer;

[0021] The mode of the optical fiber fusion splicer is modulated to single-mode-multimode mode, the discharge amount of the optical fiber fusion splicer is set to 150, and the optical fiber fusion splicer is controlled to discharge once to complete the fusion of one end of the first single-mode optical fiber and one end of the square optical fiber.

[0022] Optionally, the other end of the square optical fiber is connected to the second single-mode optical fiber in the following manner:

[0023] Place one end of the second single-mode optical fiber and the other end of the square optical fiber on a fiber fusion splicer;

[0024] The mode of the optical fiber fusion splicer is modulated to single-mode-multimode mode, the discharge amount of the optical fiber fusion splicer is set to 150, and the optical fiber fusion splicer is controlled to discharge once to complete the fusion of one end of the second single-mode optical fiber and the other end of the square optical fiber.

[0025] In a second aspect, the present application provides a knee joint angle monitoring system, comprising: a first optical fiber pigtail, a second optical fiber pigtail, a first optical fiber fixing fixture, a second optical fiber fixing fixture, and the above-mentioned square optical fiber curvature sensor;

[0026] One end of the first optical fiber pigtail is used to connect to a light source, the other end of the first optical fiber pigtail is connected to the square optical fiber curvature sensor via the first optical fiber fixing fixture, the square optical fiber curvature sensor is connected to one end of the second optical fiber pigtail via the second optical fiber fixing fixture, and the other end of the second optical fiber pigtail is used to connect to a spectrometer;

[0027] During monitoring, the square fiber curvature sensor is fixed on the knee joint of the tester, and the spectrometer is used to measure the transmission spectrum output by the square fiber curvature sensor. The interference dip wavelength of the transmission spectrum is used to characterize the rotation angle of the knee joint.

[0028] Optionally, the characterization relationship between the interference tilt wavelength and the rotation angle of the knee joint is obtained by establishing a relationship function using simulation data or experimental data.

[0029] Optionally, the relationship between the interference tilt wavelength and the rotation angle of the knee joint is a linear relationship.

[0030] According to the specific embodiments provided in this application, this application has the following technical effects.

[0031] The present application provides a square optical fiber curvature sensor and a knee joint angle monitoring system. The present application uses a square optical fiber to replace a traditional optical fiber with a circular cross-section. Since the square optical fiber light field has a rectangular distribution, when the rectangular light spot is subjected to mode excitation, since the rectangular light spot has uniform energy, a large amount of light on both sides of the light spot can be excited to a high-order mode, thereby forming interference, thereby improving the sensitivity of the sensor. In addition, the present application sets an etched cavity in the square optical fiber to form a Fabry-Perot resonant cavity, thereby further improving the sensitivity of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0033] Figure 1 This is a structural schematic diagram of a square optical fiber curvature sensor provided in one embodiment of the present application.

[0034] Figure 2 A schematic diagram of a square optical fiber cross-section provided in one embodiment of the present application.

[0035] Figure 3 This is an image of a square optical fiber fusion splicer provided in one embodiment of the present application.

[0036] Figure 4 This is a simulation diagram of the multimode optical fiber transmission spot and cross section provided in one embodiment of the present application.

[0037] Figure 5 A simulation diagram of a square optical fiber transmission spot and cross section provided in one embodiment of the present application.

[0038] Figure 6 A simulation diagram of the light field distribution of a square optical fiber cross section after etching provided in one embodiment of the present application.

[0039] Figure 7This is a schematic diagram of the structure of a square optical fiber curvature sensor with different etching depths in the single-mode and square-core optical fiber fusion zone provided by an embodiment of the present application and its corresponding light field distribution diagram.

[0040] Figure 8 This is a schematic diagram of the structure of a square optical fiber curvature sensor with different etching depths at the center of a square core optical fiber provided by an embodiment of the present application and its corresponding light field distribution diagram.

[0041] Figure 9 This is a schematic diagram of the structure of a square optical fiber curvature sensor with different etching widths at the center of a square core optical fiber provided by an embodiment of the present application and its corresponding light field distribution diagram.

[0042] Figure 10 Schematic diagram of the deformation of the etched cavity when the sensor provided in one embodiment of the present application is bent.

[0043] Figure 11 A schematic structural diagram of a knee joint angle monitoring system provided in one embodiment of the present application.

[0044] Figure 12 A graph showing the shift of the interference dip wavelength (Y) as the rotation angle (A) changes according to an embodiment of the present application.

[0045] Figure 13 A fitting curve diagram of the rotation angle (A) and the interference tilt wavelength (Y) provided in one embodiment of the present application. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0047] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0048] In order to solve the problems existing in traditional optical fiber curvature sensors, the embodiments of the present application propose to use square optical fibers to replace traditional optical fibers with circular cross-sections. Since the square optical fiber light field has a rectangular distribution. Therefore, when the rectangular light spot is subjected to mode excitation, since the rectangular light spot has uniform energy, a large amount of light on both sides of the light spot can be excited to high-order modes, thereby forming interference and improving the sensitivity of the sensor. It has a very good effect when applied to medical sensing, especially bending detection of knee joints. The square optical fiber curvature sensor provided in the embodiments of the present application provides a method for the preparation of high-precision optical fiber sensing, especially miniaturized high-excitation optical fiber sensors.

[0049] In an exemplary embodiment, a square optical fiber curvature sensor is provided, such as Figure 1 As shown, it includes: a first single-mode optical fiber 2, a square optical fiber 3 and a second single-mode optical fiber 4; the first single-mode optical fiber 2 is connected to one end of the square optical fiber 3, and the other end of the square optical fiber 3 is connected to the second single-mode optical fiber 4; Figure 2 As shown, the square optical fiber 3 includes: a square core, and a cladding wrapping the square core, and an etched cavity is etched on the cladding.

[0050] It is worth noting that the present invention uses a femtosecond laser to finely cut the middle of the square fiber to achieve the excitation of high-order modes. The cross-sectional distribution of the square fiber is as follows: Figure 2 As shown in Figure 1, the key component of the square fiber curvature sensor is a Mach-Zehnder interferometer structure consisting of a square fiber and two single-mode fibers directly connected. The core diameter d1 of the square fiber used is 50 μm, the first cladding diameter d2 is 100 μm, and the second cladding diameter d3 is 250 μm. Figure 2 shown.

[0051] Use a fiber fusion splicer to fuse square optical fibers between two single-mode optical fibers. Figure 1 It can be seen that the core diameter of the square optical fiber is much larger than that of the single-mode optical fiber, which means that its mode field diameter does not match the mode field diameter of the single-mode optical fiber. This core diameter mode field mismatch will cause the fundamental mode of the single-mode optical fiber to be excited to the higher-order mode in the square optical fiber. The embodiment of the present application welds the single-mode optical fiber and the square optical fiber through a special welding mode for multi-mode optical fibers. The control of the discharge amount is also very critical. Too small a discharge amount cannot weld the optical fibers, while too large a discharge amount will damage the optical fiber end face and increase the loss. The mode modulation of the welding machine is single-mode-multimode mode, the discharge amount is 150, and the automatic mode discharges once, such as Figure 3 shown.

[0052] In this embodiment, during preparation, the square optical fiber 3 and the first single-mode optical fiber 2 are placed on a fiber fusion splicer, as shown in FIG. Figure 3As shown in (a) in the figure. The mode modulation of the optical fiber fusion splicer is single mode-multimode mode, the discharge amount is set to 150, and the discharge is performed once. The image after fusion is shown in Figure 3 Similarly, the other end of the square optical fiber 3 and the second single-mode optical fiber 4 are placed on the optical fiber fusion splicer, the discharge amount is set to 150, the discharge mode is single-mode-multimode mode, and the number of discharges is 1.

[0053] The first single-mode optical fiber 2 is connected to the broadband light source 1 through an FC / APC connector, and the second single-mode optical fiber 4 is connected to the spectrometer 5 through an FC / APC connector. Figure 1 shown.

[0054] The sensor proposed in the embodiment of the present application is simulated by the finite element method. First, the light transmission characteristics of the multimode optical fiber and the square optical fiber are simulated. The simulation results are as follows: Figure 4 and Figure 5 As shown, Figure 4 (a) and (b) are the multimode fiber transmission spot diagram and cross-sectional simulation diagram, respectively. Figure 5 (a) and (b) are the square fiber transmission spot diagram and cross-sectional simulation diagram respectively. First, compared with the multimode fiber with a circular cross-sectional distribution (the spot is Gaussian), the square fiber spot is closer to a rectangle, indicating that the square fiber output spot quality energy is more concentrated and more uniform. Secondly, the square fiber spot presents a rectangular distribution. Compared with the Gaussian spot, small distance etching (etching cavity) will cause more light excitation and coupling ( Figure 4 、 Figure 5 The cross section of the traditional optical fiber is circular, as shown in the shaded area. Figure 4 As shown in FIG, the shape of the light field transmitted in the optical fiber is Gaussian. When the mode is excited, the energy of the light field distribution of this Gaussian shape is relatively low on both sides of the Gaussian curve, so the energy of the light excited to the higher-order mode is also relatively low, resulting in weak energy of the excitation light and low sensor sensitivity. The embodiment of the present application proposes to use square optical fiber to replace the traditional optical fiber with a circular cross section, such as Figure 5 As shown in the figure, the square fiber light field has a rectangular distribution. Therefore, when the rectangular spot is used for mode excitation, due to the uniform energy of the rectangular spot, a large amount of light on both sides of the spot can be excited into high-order modes, thus forming interference and improving the sensitivity of the sensor.

[0055] The simulation results of the etched square optical fiber are as follows: Figure 6As shown. The etched structure exposes the core, and part of the light leaked into the cladding is restricted back to the core by the air cavity, while the other part continues to leak into the air, transmitted between the two walls of the air cavity, and interferes with the light transmitted from other directions at the subsequent second single-mode optical fiber 4 fusion position, forming a Fabry-Perot resonant cavity. In order to enhance the interference effect and improve the sensitivity of the sensor, the entire cladding is etched to completely expose the core. This means that the core is completely exposed, the single-mode light is effectively leaked and excited into a high-order mode, and the cladding is completely etched, so that the large mode field range of the leaked light can cover all claddings and experience all cladding refractive indices, so that the high-order modes are more fully excited and transmitted separately, and finally coupled to obtain extremely high sensitivity. The width of the etched opening should not be too long, because the transmission of light in the air will cause great loss. Combined with previous studies and the overall interference length, the etched width is selected to be 40μm. In the embodiment of the present application, the etching depth and etching width are exemplary values, and in some cases they can be adjusted according to actual conditions.

[0056] In an exemplary embodiment, the parameter information of the etched cavity is determined using the following formula:

[0057]

[0058] Where, I is the interference light intensity of the square fiber, I clad is the light intensity of the cladding mode of the square fiber, I core is the light intensity of the core mode of the square fiber, φ is the phase difference between the core mode and the cladding mode of the square fiber, I clad Related to the parameter information of the etched cavity, I clad The relationship function with the parameter information of the etched cavity is obtained by establishing a relationship model through simulation data or experimental data.

[0059] I clad =I F-P +I clad其他 ;

[0060] Among them, I F-P and I clad其他 They are the light intensity of the mode that enters the fiber cladding after passing through the square fiber etched cavity and other cladding modes. F-P They are related to the position, depth and width of the etched cavity. When the etching conditions are different, it will affect I F-P distribution, which ultimately causes the interference light intensity of the interferometer to change.

[0061] φ represents the phase difference between the core mode and the cladding mode:

[0062]

[0063] Among them, Δneff is the effective refractive index difference between the cladding mode and the core mode, L is the interference path length of the Mach-Zehnder interferometer, and λ is the wavelength of the input light. For the square fiber curvature sensor, the square fiber is 3 cm long and is precisely cut into the cladding using a femtosecond laser, with controlled cut width and depth.

[0064] The fiber cutting position and depth have a great influence on the performance of the sensor. Different etching widths and depths will affect the sensing characteristics of the sensor. When the etching position is in the single-mode and square-core fiber fusion zone, and the etching width is 30μm and the depth is 37.5um, 75um, and 100um respectively, the sensor structure diagram and the corresponding light field distribution diagram are as follows: Figure 7 As shown, Figure 7 (a)-(c) are schematic diagrams of the sensor structure when the etching position is in the fusion zone of single-mode and square-core fiber, the etching width is 30μm, and the etching depth is 37.5um, 75um, and 100um respectively. Figure 7 (d)-(f) in Figure 7 The square distribution diagram corresponding to (a)-(c) in .

[0065] Depend on Figure 7 It can be seen that as the etching depth increases, the more high-order modes excited by the square fiber, the higher the sensitivity of the sensor. When the etching position is at the center of the square fiber, and the etching width is 30μm, and the depth is 37.5um, 75um, and 100um respectively, the sensor structure diagram and the corresponding light field distribution diagram are as follows: Figure 8 As shown, Figure 8 (a)-(c) are schematic diagrams of the sensor structure when the etching position is at the center of the square core fiber, the etching width is 30μm, and the depth is 37.5um, 75um, and 100um respectively. Figure 8 (d)-(f) in the figure are respectively Figure 8 The square distribution diagram corresponding to (a)-(c) in .

[0066] contrast Figure 7 and Figure 8 It can be seen that when the etching position is different, the light field distribution of the sensor is different, resulting in different sensor sensitivities. Figure 7 (f) and Figure 8 (f) It can be seen that when the etching position is at the center of the square fiber, the air cavity has a stronger ability to excite high-order modes. When the etching position is at the center of the square fiber, and the etching depth is 100um, the width is 30um, 40um, and 50um respectively, the sensor structure diagram and its corresponding light field distribution are as follows: Figure 9 As shown, Figure 9(a)-(c) are schematic diagrams of the sensor structure when the etching position is at the center of the square core fiber, the etching depth is 100um, and the width is 30um, 40um, and 50um respectively. Figure 9 (d)-(f) in the figure are respectively Figure 9 Light field distribution diagram corresponding to (a)-(c) in the figure.

[0067] Depend on Figure 9 It can be seen that as the etching width increases, the distribution of the light field also changes, and the cavity does not simply enhance the excitation of high-order modes. Figure 9 (e) and (f) show that the distribution of the light field does not change much as the etching width increases, indicating that the etching cavity has a certain threshold for the excitation of high-order modes. Figure 7-Figure 9 It can be seen that by changing the position of the etched cavity and the etching depth and width, the light transmission characteristics of the sensor can be changed, thereby adjusting the sensitivity of the sensor.

[0068] In addition, a cavity with a certain depth and width is etched in the square optical fiber. Since the refractive index of the optical fibers at both ends of the etched cavity is higher than that of the air, and the optical fibers at both ends are smoothly distributed, the fiber walls on both sides and the etched cavity form a small Fabry-Perot interferometer cavity. Figure 7 (d)-(f) show that as the etching depth increases, the ability of the air cavity formed by etching to achieve interference becomes stronger ( Figure 7 The area with two white lines in (f)). Figure 7-Figure 9 It can be seen that the interference ability of the Fabry-Perot interferometer cavity formed by etching will change with the etching depth, etching width and etching position. In practical applications, due to the bending of the optical fiber sensor, the angles of the two walls of the Fabry-Perot interferometer cavity are tilted, which changes the characteristics of the light transmitted in the cavity and affects the characteristics of the entire sensor, such as Figure 10 In order to ensure the existence of the Fabry-Perot interference cavity, the etching width should not be too long. In combination with previous research and the obvious overall interference effect, the embodiment of the present application selects an etching width of 40μm.

[0069] In another exemplary embodiment, the length of the square optical fiber is determined using the following formula:

[0070]

[0071] Where FSR is the free spectral range, λ0 is the wavelength of the interference valley, Δn eff is the effective refractive index of the square fiber, and L is the interference length of the square fiber.

[0072] For a fiber Mach-Zehnder interferometer, its free spectral range (FSR) characterizes the wavelength difference between the two interference valleys. It can be seen that under the condition that the effective refractive index of the optical fiber is fixed, the FSR is only related to the interference length. A smaller interference length can obtain a larger FSR, and a larger interference length will make the intervals between the interference valleys very small. In order to obtain a large-scale measurement of the entire knee joint, the interference length of the sensor must be controlled. The embodiment of the present application selects a 3cm square optical fiber as the length of the sensor (since the refractive index distribution of the square optical fiber is not fixed, the length of the square optical fiber is not fixed to the existing size).

[0073] In an exemplary embodiment, a knee joint angle monitoring system is provided, such as Figure 11 As shown, the apparatus comprises: a first optical fiber pigtail 101, a second optical fiber pigtail 102, a first optical fiber fixing fixture 103, a second optical fiber fixing fixture 104, and a square optical fiber curvature sensor 105. The two ends of the square optical fiber curvature sensor 105 are connected to the first optical fiber fixing fixture 103 and the second optical fiber fixing fixture 104, respectively. The first optical fiber fixing fixture 103 is connected to the first optical fiber pigtail 101, and the second optical fiber fixing fixture 104 is connected to the second optical fiber pigtail 102. The two optical fiber pigtails are connected to a spectrometer and a broadband light source, respectively. The first optical fiber fixing fixture 103 and the second optical fiber fixing fixture 104 are fixed on both sides of the knee joint to fix the square optical fiber curvature sensor 105. When the knee joint bends, the square optical fiber curvature sensor bends, and the spectrum of the square optical fiber curvature sensor changes accordingly. The bending angle of the knee joint can be obtained through spectral measurement.

[0074] During the measurement process, the knee bends, causing the tibia to move relative to the thigh, which corresponds to the square fiber curvature sensor. The angle changes as the knee moves. Between 0° and 90°, the transmission spectrum of the square fiber curvature sensor undergoes a significant wavelength shift. By quantifying the wavelength shift, the angle change of the sensor is reflected, thereby evaluating the angle change of the knee bending. Figure 12 As shown, with the bending angle ( Figure 11 The wavelength of the interference dip angle of the sensor shifts from 1565.3467nm to 1554.4677nm, with a total shift of 10.879nm. The fitting relationship between the wavelength of the interference dip angle and the rotation angle is shown in the figure below: Figure 13 The square fiber curvature sensor has an angular sensitivity of up to 128 pm / ° and a linearity of 0.96.

[0075] The databases involved in the various embodiments provided herein may include at least one of a relational database and a non-relational database. Non-relational databases may include, but are not limited to, distributed databases based on blockchains. The processors involved in the various embodiments provided herein may include, but are not limited to, general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic units, data processing logic units based on quantum computing, and the like.

[0076] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0077] This document uses specific examples to illustrate the principles and implementation methods of this application. The description of the above examples is only intended to help understand the method and core concept of this application. At the same time, for those skilled in the art, based on the concept of this application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A square optical fiber curvature sensor, characterized in that: include: a first single-mode optical fiber, a square optical fiber, and a second single-mode optical fiber; The first single-mode optical fiber is connected to one end of the square optical fiber, and the other end of the square optical fiber is connected to the second single-mode optical fiber; The square optical fiber includes: a square fiber core and a cladding wrapping the square fiber core, wherein an etched cavity is etched on the cladding.

2. The square optical fiber curvature sensor according to claim 1, characterized in that: The cladding includes a first cladding and a second cladding, wherein the first cladding is wrapped around the outside of the square core, and the second cladding is wrapped around the outside of the first cladding.

3. The square optical fiber curvature sensor according to claim 2, characterized in that: The diameter of the square core is 50 μm, the diameter of the first cladding is 100 μm, and the diameter of the second cladding is 250 μm.

4. The square optical fiber curvature sensor according to claim 1, characterized in that: The parameter information of the etching cavity is determined by the following formula: Where, I is the interference light intensity of the square fiber, I clad is the light intensity of the cladding mode of the square fiber, I core is the light intensity of the core mode of the square fiber, φ is the phase difference between the core mode and the cladding mode of the square fiber, I clad Related to the parameter information of the etched cavity, I clad The relationship function with the parameter information of the etched cavity is obtained by establishing a relationship model through simulation data or experimental data.

5. The square optical fiber curvature sensor according to claim 1, characterized in that: The length of the square optical fiber is determined by the following formula: Where FSR is the free spectral range, λ0 is the wavelength of the interference valley, Δn eff is the effective refractive index of the square fiber, and L is the interference length of the square fiber.

6. The square optical fiber curvature sensor according to claim 1, characterized in that: The first single-mode optical fiber is connected to one end of the square optical fiber in the following manner: Placing one end of the first single-mode optical fiber and one end of the square optical fiber on a fiber fusion splicer; The mode of the optical fiber fusion splicer is modulated to single-mode-multimode mode, the discharge amount of the optical fiber fusion splicer is set to 150, and the optical fiber fusion splicer is controlled to discharge once to complete the fusion of one end of the first single-mode optical fiber and one end of the square optical fiber.

7. The square optical fiber curvature sensor according to claim 1, characterized in that: The other end of the square optical fiber is connected to the second single-mode optical fiber in the following manner: Place one end of the second single-mode optical fiber and the other end of the square optical fiber on a fiber fusion splicer; The mode of the optical fiber fusion splicer is modulated to single-mode-multimode mode, the discharge amount of the optical fiber fusion splicer is set to 150, and the optical fiber fusion splicer is controlled to discharge once to complete the fusion of one end of the second single-mode optical fiber and the other end of the square optical fiber.

8. A knee joint angle monitoring system, characterized in that: include: A first optical fiber pigtail, a second optical fiber pigtail, a first optical fiber fixing fixture, a second optical fiber fixing fixture, and the square optical fiber curvature sensor according to any one of claims 1 to 7; One end of the first optical fiber pigtail is used to connect to a light source, the other end of the first optical fiber pigtail is connected to the square optical fiber curvature sensor via the first optical fiber fixing fixture, the square optical fiber curvature sensor is connected to one end of the second optical fiber pigtail via the second optical fiber fixing fixture, and the other end of the second optical fiber pigtail is used to connect to a spectrometer; During monitoring, the square fiber curvature sensor is fixed on the knee joint of the tester, and the spectrometer is used to measure the transmission spectrum output by the square fiber curvature sensor. The interference dip wavelength of the transmission spectrum is used to characterize the rotation angle of the knee joint.

9. The knee joint angle monitoring system according to claim 8, characterized in that: The characterization relationship between the interference tilt wavelength and the rotation angle of the knee joint is obtained by establishing a relationship function using simulation data or experimental data.

10. The knee joint angle monitoring system according to claim 8 or 9, characterized in that: The relationship between the interference tilt wavelength and the rotation angle of the knee joint is linear.

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