Asymmetric U-shaped optical fiber taper sensing probe, preparation method thereof and sensor

Abstract

The invention discloses an asymmetric U-shaped optical fiber taper sensing probe, a preparation method thereof and a sensor, and the asymmetric U-shaped optical fiber taper sensing probe comprises an asymmetric U-shaped optical fiber taper and a PDMS cladding for packaging the asymmetric U-shaped optical fiber taper; wherein the asymmetric U-shaped optical fiber taper comprises two taper transition areas and an asymmetric U-shaped taper waist area located between the two taper transition areas. The asymmetric U-shaped optical fiber taper sensing probe has the advantages of being thin in waist diameter and good in stability, has good stress and temperature response characteristics when being used for a sensor, and has important application prospects in the fields of safety monitoring, aerospace, medical treatment and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber sensors, and in particular relates to an asymmetric U-shaped optical fiber cone sensing probe and a preparation method and a sensor thereof. Background Art

[0002] As an important parameter in safety monitoring, aerospace and medical fields, accurate measurement of stress plays a vital role in monitoring the deformation of bridges and tunnels, aircraft manufacturing and damage in minimally invasive surgery. Fiber optic stress sensors have been widely used for accurate measurement of stress due to their small size, strong anti-electromagnetic interference ability, easy integration into the tip of intracavitary medical devices, and large-area laying inside the structure.

[0003] For example, fiber Bragg gratings are integrated into the tip of intracavitary surgical tools to sense the force generated by the tool interacting with human tissue when entering the cavity, thereby effectively avoiding damage to healthy tissue caused by the tool. However, the stress sensitivity of this type of sensor is low, only ~10pm / N. Mach-Zehnder fiber stress sensors have attracted much attention because they have a strong evanescent field and are sensitive to external stress changes. This type of sensor is usually prepared by methods such as offset welding and fused taper, but this type of fiber sensor is not packaged and protected. Because the fiber cone is thin and easy to break at the offset, the mechanical strength of this type of sensor is poor, which seriously limits its application in real life.

[0004] In order to further improve the mechanical strength of the Mach-Zehnder sensing structure, researchers have prepared sensor devices by integrating flexible materials with optical fibers. For example, in 2015, Yang et al. proposed using polydimethylsiloxane (PDMS) to completely wrap the S-shaped optical fiber cone to prepare stress and temperature sensors ("PDMS-Coated S-Tapered Fiber for Highly Sensitive Measurements of Transverse Load and Temperature", IEEE Sensors Journal, 2015, 15: 3429-3435.). Since PDMS has a lower Young's modulus, the PDMS-coated optical fiber has better sensitivity and mechanical strength, and its stress sensitivity is -29.03nm / N. At the same time, PDMS has a larger thermo-optical coefficient and thermal expansion coefficient, and its temperature sensitivity reaches -2.17nm / ℃. In 2024, Wang et al. proposed an ultra-microfiber intelligent sensor based on polymer materials ("Optical Microfiber Intelligent Sensor: Wearable Cardiorespiratory and Behavior Monitoring with a Flexible Wave-Shaped Polymer Optical Microfiber", ACS Applied Materials & Interfaces, 2024, 16: 8333-8345.), the polymer ultra-microfiber formed a flexible waveform structure, successfully carried out cardiopulmonary and behavioral detection experiments, showing the high sensitivity and stability potential of polymer sensors in performing wearable tasks. In the same year, Zhang et al. proposed the use of plastic optical fiber and PDMS to prepare a new type of portable wearable cardiopulmonary sensor ("Wearable Cardiorespiratory Sensor for Real-Time Monitoring With Smartphone Integration", IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, 73, 2024, 700-710), which achieved accurate measurement of multiple parameters such as respiratory rate and heart rate. Summary of the invention

[0005] Based on the above technical problems, the present invention provides an asymmetric U-shaped fiber optic cone sensing probe, a preparation method and a sensor thereof. The asymmetric U-shaped fiber optic cone sensing probe has the advantages of thin waist diameter and good stability. When used as a sensor, it has good stress and temperature response characteristics, and has important application prospects in safety monitoring, aerospace, medical and other fields.

[0006] The present invention provides an asymmetric U-shaped optical fiber cone sensing probe, comprising an asymmetric U-shaped optical fiber cone and a PDMS cladding encapsulating the asymmetric U-shaped optical fiber cone;

[0007] The asymmetric U-shaped optical fiber taper includes two tapered transition regions and an asymmetric U-shaped taper waist region located between the two tapered transition regions.

[0008] Preferably, the asymmetric U-shaped optical fiber cone has a length of 2-5 mm and a diameter of 60-80 μm.

[0009] Preferably, the thickness of the PDMS cladding is 800-1500 μm.

[0010] The present invention also provides a method for preparing the above-mentioned asymmetric U-shaped optical fiber cone sensing probe, comprising the following steps:

[0011] S1, after fusing two sections of optical fiber, draw them into a cone to obtain a linear optical fiber cone;

[0012] S2, bending the non-middle part of the waist of the linear optical fiber cone into a U shape to obtain an asymmetric U-shaped optical fiber cone;

[0013] S3, wrapping the surface of the asymmetric U-shaped optical fiber cone with PDMS optical glue, and after curing, obtaining the asymmetric U-shaped optical fiber cone sensing probe.

[0014] In the present invention, an asymmetric U-shaped optical fiber cone is first prepared by a simple melt-tap and bending technique, and then the asymmetric U-cone optical fiber cone is completely wrapped with PDMS to effectively improve the mechanical strength of the probe; since PDMS has a lower Young's modulus and a higher thermo-optic coefficient, the stress sensitivity of the two interference peaks reaches 142.27nm / N and 60.88nm / N, and the temperature sensitivity is -0.73187nm / ℃ and -0.55989nm / ℃, respectively.

[0015] Preferably, step S1 specifically comprises: after fusing two sections of multimode optical fiber with the cladding removed, stretching one section of the optical fiber axially outward from the fusion point in a molten state until the fusion-spliced ​​optical fiber is stretched into a cone, thereby obtaining the linear optical fiber cone.

[0016] Preferably, step S2 specifically comprises: after heating and melting the non-middle part of the waist of the linear optical fiber cone, bending both ends of the linear optical fiber cone inward until the two ends are parallel, so as to obtain the asymmetric U-shaped optical fiber cone.

[0017] Preferably, step S3 specifically comprises: mixing PDMS prepolymer and curing agent to form PDMS optical glue, immersing the asymmetric U-shaped optical fiber cone in the PDMS optical glue, and heating and curing to obtain the asymmetric U-shaped optical fiber cone.

[0018] Preferably, the mass ratio of the PDMS prepolymer to the curing agent is 5-15:1;

[0019] Preferably, the heating curing temperature is 50-70° C. and the time is 20-40 min.

[0020] The present invention also proposes a sensor based on an asymmetric U-shaped optical fiber cone sensing probe, which includes the asymmetric U-shaped optical fiber cone sensing probe mentioned above or the asymmetric U-shaped optical fiber cone sensing probe prepared by the above preparation method.

[0021] Preferably, the sensor further comprises a broadband light source and a spectrum analyzer;

[0022] The broadband light source and the spectrum analyzer are respectively connected to two conical transition areas of the asymmetric U-shaped optical fiber cone sensing probe.

[0023] The specific working principle of the sensor of the present invention is as follows:

[0024] The incident light is split into two beams at one end of the asymmetric U-shaped fiber cone. One beam is transmitted forward along the asymmetric U-shaped fiber cone, while the other beam is transmitted in PDMS. The two beams are coupled at the other end of the asymmetric U-shaped fiber cone, and interference superposition forms a Mach-Zehnder interference spectrum. The transmitted light intensity of the interference spectrum can be written as:

[0025]

[0026] I1 represents the intensity of the core mode, I2 m represents the light intensity of the m-order cladding mode, is the phase difference between the two, expressed as follows:

[0027]

[0028] here, is the effective refractive index difference, λ is the wavelength of the incident light, L eff is the effective interference length of the asymmetric U-shaped optical fiber cone area; the central wavelength corresponding to the interference peak and trough can be expressed as follows:

[0029]

[0030] Both PDMS and silica materials have thermo-optical effect and thermal expansion effect, and PDMS has a lower Young's modulus. According to formula (3), the effective refractive index difference and interference length of the probe change with the change of stress and temperature, and the central wavelength of the interference peak drifts with the change of stress and temperature.

[0031] The invention provides an asymmetric U-shaped optical fiber cone sensing probe and a preparation method and a sensor thereof, which can be used for simultaneously and effectively measuring stress and temperature.

[0032] The present invention first uses melting technology to prepare the fiber cone, and bends the fiber cone to prepare an asymmetric U-shaped fiber cone (cone + U-shaped structure). On the one hand, the fiber cone has a compact structure and is more convenient in actual use. On the other hand, compared with the traditional linear fiber cone (cone + linear structure), the U-shaped structure of the fiber cone of the present invention has greater deformability in stress conduction and higher stress measurement sensitivity; secondly, the asymmetric U-shaped fiber cone is completely wrapped with PDMS, and the mechanical strength of the resulting sensing probe is increased; the resulting asymmetric U-shaped fiber cone sensing probe has a thin waist diameter and good stability. In the entire preparation process, only one fiber fusion splicer and one temperature control box are used, which is low in cost and simple in preparation process. In addition, since PDMS has a smaller Young's modulus and a higher thermo-optic coefficient, the resulting sensing probe has better stress and temperature response characteristics.

[0033] The present invention tests the variation of two interference peaks in the interference spectrum of the sensor probe with stress and temperature. The stress sensitivities of interference peaks A and B are 142.27 nm / N and 60.88 nm / N, respectively, and the temperature sensitivities are -0.73187 nm / °C and -0.55989 nm / °C, respectively. The stress and temperature can be measured simultaneously by using the sensor matrix method.

[0034] The asymmetric U-shaped optical fiber cone sensing probe of the present invention has the characteristics of high mechanical strength, simple preparation process and low cost, and has important application prospects in the fields of safety monitoring, aerospace and medical treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a schematic diagram of the preparation process of the asymmetric U-shaped optical fiber cone sensing probe of the present invention;

[0036] Figure 2 The following are the physical pictures of the asymmetric U-shaped fiber cone sensing probe of the present invention: (a) is a physical picture of a linear fiber cone, (b) is a physical picture of an asymmetric U-shaped fiber cone, and (c) is a physical picture of an asymmetric U-shaped fiber cone sensing probe;

[0037] Figure 3The interference spectrum of the asymmetric U-shaped optical fiber cone sensing probe of the present invention at 30°C;

[0038] Figure 4 A schematic diagram of a sensor based on an asymmetric U-shaped optical fiber cone sensing probe according to the present invention;

[0039] Figure 5 The stress response characteristic diagram of the asymmetric U-shaped optical fiber cone sensing probe of the present invention: (a) is the transmission interference spectrum under different stresses, and (b) is the linear fitting result of the central wavelengths of peaks A and B under different stresses;

[0040] Figure 6 The temperature response characteristic diagram of the asymmetric U-shaped optical fiber cone sensor probe of the present invention: (a) is the transmission interference spectrum at different temperatures, and (b) is the linear fitting result of the central wavelength of peaks A and B at different temperatures. DETAILED DESCRIPTION

[0041] Hereinafter, the present invention will describe the technical solution in detail through specific embodiments, but it should be clearly stated that these embodiments are for illustration only and are not to be construed as limiting the scope of the present invention.

[0042] Example

[0043] Reference Figure 1 This embodiment provides an asymmetric U-shaped optical fiber cone sensor probe which is prepared by the following method:

[0044] (1) Splicing two multimode optical fibers

[0045] Take two sections of multimode optical fiber (Corning 676520) with a core diameter of 62.5μm, strip the cladding with a fiber stripping pliers, cut the end surface flat and fix it in the V-groove of the fusion splicer, and use the multimode optical fiber automatic fusion splicing program to fuse the two sections of multimode optical fiber together. The structure is as follows: Figure 1 (a)

[0046] (2) Preparation of multimode fiber tapers

[0047] The multimode optical fiber after fusion was manually discharged with a discharge intensity of 61bit and a discharge time of 2s. During the discharge, one end of the optical fiber was kept fixed and an external force was applied to the other end of the optical fiber to make it move at a uniform speed, thereby preparing a uniform cone. After multiple manual discharges, a linear optical fiber cone with a length of 3.5mm was obtained (the length of the cone transition zone was 400μm, the length of the cone waist zone was 3.1mm, and the diameter of the cone waist zone was 85μm). The results are as follows Figure 1 (b)

[0048] (3) Preparation of asymmetric U-shaped fiber tapers

[0049] First, fix the linear fiber cone on the fixture of the lifting platform. The lifting platform consists of two three-dimensional mobile platforms placed side by side. The distance between the two platforms is 10 cm, and the initial height is 20 cm. The fiber cone is suspended between the two platforms. Place the alcohol lamp below the fiber cone, adjust the position of the alcohol lamp so that the outer flame can just act on the one-third of the waist of the linear fiber cone. While not changing the position of the fiber cone, apply force to the optical fibers at both ends of the linear fiber cone, so that the optical fibers move slowly upward and inward. When the two sections of the optical fiber are parallel to each other, remove the alcohol lamp to obtain an asymmetric U-shaped fiber cone. The results are as follows: Figure 1 (c)

[0050] (4) Preparation of PDMS-encapsulated asymmetric U-shaped fiber cone

[0051] First, the asymmetric U-shaped fiber cone is suspended and fixed above the lifting platform, and the U-shaped mold is fixed on the platform below the lifting platform. The lifting platform is adjusted to allow the asymmetric U-shaped fiber cone to enter the U-shaped mold. The asymmetric U-shaped fiber cone is about 2mm away from the bottom of the mold. The main component of the mold is polyethylene, the height is 1cm, and the diameter of the tube mouth is 1cm.

[0052] PDMS prepolymer (SYLGARD TM 184) and a curing agent in a ratio of 10:1 to form PDMS optical glue, and then drip it into the U-shaped mold. The PDMS optical glue just fills the mold, and the asymmetric U-shaped optical fiber cone is completely immersed in the PDMS optical glue. Then, it is heated at 60°C for 30 minutes. The silicon oxygen bonds (Si-O-Si) of the prepolymer molecules in the PDMS optical glue are broken and a three-dimensional network is formed. At this time, the PDMS optical glue is completely cured. After being taken out of the temperature control box, the U-shaped mold shell is removed with tweezers to obtain the PDMS-encapsulated asymmetric U-shaped optical fiber cone, which is the asymmetric U-shaped optical fiber cone sensing probe. The results are as follows: Figure 1 As shown in (d).

[0053] The optical photo of the asymmetric U-shaped fiber cone sensor probe obtained in this embodiment is shown in FIG. Figure 2 As shown, from Figure 2 It can be seen from the figure that the sensor probe has a regular structure and good light transmittance.

[0054] The two ends of the asymmetric U-shaped fiber cone sensor probe obtained in this embodiment are connected to fiber pigtails, and then connected to a broadband light source (SC-5-FC) and a spectrum analyzer (AQ6370D). The transmission interference spectrum of the structure is recorded at a temperature of 30°C. The results are shown in FIG. Figure 3 As shown. Figure 3 It can be seen that there are multiple resonance peaks in the interference spectrum, and the maximum contrast is about 10dB.

[0055] The asymmetric U-shaped fiber cone sensor probe obtained in this example was used to build a stress and temperature test device. The experimental device consisted of a broadband light source (SC-5-FC), a spectrum analyzer (AQ6370D), a programmable temperature control box (Kingjo, CK-80G) and a weight. The results are shown in Figure 2. Figure 4 shown.

[0056] In order to test the stress and temperature response characteristics of the asymmetric U-shaped optical fiber cone sensing probe obtained in this embodiment, the stress response characteristics are first studied:

[0057] The asymmetric U-shaped fiber cone sensor probe is fixed on the storage table of the temperature control box, and the two ends of the asymmetric U-shaped fiber cone sensor probe are respectively connected to a broadband light source and a spectrum analyzer;

[0058] Five weights are placed on top of the asymmetric U-shaped fiber cone sensor probe. The mass of each weight is 0.5g, and the corresponding stress is 5mN. The stress applied to the probe increases from 0mN to 25mN, with a step length of 5mN.

[0059] The transmission interference spectrum of the asymmetric U-shaped fiber cone sensor probe under different stresses is recorded. The results are as follows Figure 5 As shown;

[0060] Depend on Figure 5 (a) It can be seen that with the increase of stress, multiple interference peaks in the interference spectrum move toward the long wavelength direction. This is because the Young's modulus of PDMS is small, and it undergoes more obvious deformation under stress. The effective interference length of the probe increases, and the interference peak moves toward the long wavelength direction as a whole. However, the movement amount of each interference peak is different, that is, the response to stress is different;

[0061] The movement of the two interference peaks near 1545nm (peak A) and 1565nm (peak B) with stress changes was analyzed in detail: when the stress increased from 0mN to 25mN, peaks A and B moved 3.4952nm and 1.5321nm respectively; the central wavelengths of the two interference peaks at each stress were recorded, and the stress was used as the horizontal coordinate and the central wavelength positions of the two interference peaks were used as the vertical coordinate. The two sets of data points were linearly fitted. The results are shown in Figure 5 (b) is given by Figure 5 (b) It can be seen that the stress sensitivities of peaks A and B are 142.27 nm / N and 60.88 nm / N, respectively, and the linear correlation coefficients are 0.99464 and 0.99511.

[0062] Secondly, the temperature response characteristics are studied:

[0063] The asymmetric U-shaped fiber cone sensor probe was placed in a programmable temperature control box. The temperature of the temperature control box was set to 30℃, 35℃, 40℃, 45℃, 50℃, 55℃ and 60℃ respectively. The transmission interference spectrum of the probe at each temperature was recorded in turn at intervals of 5℃. Seven sets of data were obtained. Figure 6 The interference spectrum at each temperature needs to be recorded after the temperature reaches the set value and stabilizes for 1 minute;

[0064] Depend on Figure 6 (a) It can be seen that when the temperature of the temperature control box increases from 30℃ to 60℃, peaks A and B move toward the short wavelength direction by 21.9049nm and 16.1115nm respectively;

[0065] Record the central wavelength positions of peaks A and B at each temperature and perform linear fitting on them. The fitting results are shown in Figure 6 (b) is given by Figure 6 (a) It can be seen that the temperature sensitivities of the two interference peaks of the sensor probe are -0.73187nm / ℃ and -0.55989nm / ℃ respectively, and the linear correlation coefficients are 0.99303 and 0.89771.

[0066] Since peak A and peak B have different response characteristics to stress and temperature, the sensing matrix method can be used to achieve simultaneous sensing of stress and temperature; the sensing matrix is ​​as follows:

[0067]

[0068] In the formula, Δλ A and Δλ B are the drift of the central wavelength of peak A and peak B with stress and temperature, in nm; ΔF and ΔT represent the changes of stress and temperature, in N and °C, respectively; S FA and S TA are the stress and temperature sensitivities of peak A, S FA 142.27nm / N, S TA -0.73187nm / ℃, S FB and S TB is the stress and temperature sensitivity of peak B, S FB 60.88nm / N, S TB It is -0.55989nm / ℃.

[0069] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. An asymmetric U-shaped optical fiber cone sensing probe, characterized in that: It includes an asymmetric U-shaped optical fiber cone and a PDMS cladding wrapping the asymmetric U-shaped optical fiber cone; The asymmetric U-shaped optical fiber taper includes two tapered transition regions and an asymmetric U-shaped taper waist region located between the two tapered transition regions.

2. The asymmetric U-shaped fiber cone sensing probe according to claim 1, characterized in that: The asymmetric U-shaped optical fiber cone has a length of 2-5 mm and a diameter of 60-80 μm.

3. The asymmetric U-shaped optical fiber cone sensing probe according to claim 1 or 2, characterized in that: The thickness of the PDMS cladding is 800-1500 μm.

4. A method for preparing the asymmetric U-shaped optical fiber cone sensing probe according to any one of claims 1 to 3, characterized in that: The steps include: S1, after fusing two sections of optical fiber, draw them into a cone to obtain a linear optical fiber cone; S2, bending the non-middle part of the waist of the linear optical fiber cone into a U shape to obtain an asymmetric U-shaped optical fiber cone; S3, wrapping the surface of the asymmetric U-shaped optical fiber cone with PDMS optical glue, and after curing, obtaining the asymmetric U-shaped optical fiber cone sensing probe.

5. The method for preparing the asymmetric U-shaped optical fiber cone sensing probe according to claim 4, characterized in that: Step S1 specifically includes: after fusing two sections of multimode optical fibers without cladding, one section of the optical fiber is stretched axially outward from the fusion point in a molten state until the fusion-spliced ​​optical fiber is stretched into a cone, thereby obtaining the linear optical fiber cone.

6. The method for preparing the asymmetric U-shaped optical fiber cone sensing probe according to claim 4 or 5, characterized in that: Step S2 specifically includes: heating and melting the non-middle part of the waist of the linear optical fiber cone, and then bending both ends of the linear optical fiber cone inward until the two ends are parallel, so as to obtain the asymmetric U-shaped optical fiber cone.

7. The method for preparing the asymmetric U-shaped optical fiber cone sensing probe according to any one of claims 4 to 6, characterized in that: Step S3 specifically includes: mixing PDMS prepolymer and curing agent to form PDMS optical glue, immersing the asymmetric U-shaped optical fiber cone in the PDMS optical glue, and heating and curing to obtain the asymmetric U-shaped optical fiber cone.

8. The method for preparing the asymmetric U-shaped optical fiber cone sensing probe according to claim 7, characterized in that: The mass ratio of the PDMS prepolymer to the curing agent is 5-15:1; Preferably, the heating curing temperature is 50-70° C. and the time is 20-40 min.

9. A sensor based on an asymmetric U-shaped optical fiber cone sensing probe, characterized in that: It comprises the asymmetric U-shaped optical fiber cone sensing probe according to any one of claims 1 to 3 or the asymmetric U-shaped optical fiber cone sensing probe prepared by the preparation method according to any one of claims 4 to 8.

10. The sensor based on the asymmetric U-shaped optical fiber cone sensing probe according to claim 9, characterized in that: The sensor also includes a broadband light source and a spectrum analyzer; The broadband light source and the spectrum analyzer are respectively connected to two conical transition areas of the asymmetric U-shaped optical fiber cone sensing probe.

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