Double-peanut-type tapering structure optical fiber sensor and preparation method and application thereof

Abstract

The invention belongs to the technical field of optical fiber sensing devices, and particularly relates to a double-peanut type tapering structure optical fiber sensor and a preparation method and application thereof. The optical fiber sensor comprises a first single-mode optical fiber, a multi-mode optical fiber and a second single-mode optical fiber which are connected in sequence, spherical welding surfaces of the first single-mode optical fiber and the multi-mode optical fiber form a first peanut-shaped structure, spherical welding surfaces of the multi-mode optical fiber and the second single-mode optical fiber form a second peanut-shaped structure, and a fiber core of the multi-mode optical fiber is of a tapering structure with a thin middle and two wide ends; the method comprises the following steps: respectively welding two ends of a multimode optical fiber with one ends of two single-mode optical fibers to form peanut-shaped connection, and then tapering the multimode optical fiber. The optical fiber sensor is highly sensitive to curvature change through the double-peanut-shaped tapering structure, the influence of temperature on sensing performance can be reduced, and the preparation method is simple and convenient in process, high in operability, low in cost and convenient for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensor technology, and specifically relates to a double peanut-shaped tapered fiber optic sensor, its preparation method, and its application. Background Technology

[0002] In recent years, vital sign monitoring equipment has been widely used in medical diagnosis, health management and smart wearables. As important human physiological parameters, pulse and respiration have broad application value in disease prevention, rehabilitation treatment and daily health management. Fiber optic sensors have received widespread attention in human vital sign detection due to their high sensitivity, small size and excellent resistance to electromagnetic interference. However, existing fiber optic sensors often suffer from problems such as insufficient measurement range, inability to meet the measurement needs of different situations, and interference from changes in ambient temperature, which affects the detection accuracy when monitoring respiration and pulse signals.

[0003] In the prior art, Wei Qingchao et al. designed a flexible curvature sensor (Wei Qingchao, Zhou Shuguang. Design of a flexible curvature sensor based on SMF-PDMS-DCF [J]. Instrumentation Technology and Sensors, 2024, 02). This sensor uses polydimethylsiloxane flexible material as a coupler to connect single-mode optical fiber and dual-core optical fiber. Experiments showed that the curvature ranged from 0 to 4.1198 m. －1 At that time, based on the relationship between spectral intensity and curvature, the sensitivity was -1.6715 dB / m. -1 Although this sensor has a simple structure and is flexible, it has low sensitivity, and the polydimethylsiloxane material used is very sensitive to temperature changes, failing to solve the problem of temperature cross-sensitivity.

[0004] In existing technologies, Min Shao et al. designed a wearable respiratory sensor (Wearable respiratory sensor based on Mach-Zehnder interferometer in seven-core fiber[J]. Optics & Laser Technology, 2024, 174: 110662), which achieves the sensor's operation in the 0-4.66m range by placing a seven-core optical fiber between two single-mode optical fibers and splicing them together to form a gourd-shaped structure. -1 The maximum sensitivity within the curvature range is -7.039 dB / m. -1 The low-temperature cross-sensitivity is -0.03m. -1 / ℃; The sensor is embedded in a flexible textile strip and worn on the human body to monitor human respiration; The sensor has the advantages of high sensitivity and comfortable wear, and also solves the problem of temperature crosstalk to the sensor. However, the sensitivity still needs to be improved. It cannot accurately detect some slight bends, and it does not achieve different sensitivities for different curvature ranges, so it cannot be used for different situations. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention aims to propose a double peanut-shaped tapered fiber optic sensor, its fabrication method, and its application. This fiber optic sensor, through its double peanut-shaped tapered structure design, makes the sensor highly sensitive to curvature changes, exhibiting different sensitivities within different curvature ranges. This allows the fiber optic sensor to have greater dynamic range and sensitivity adjustment capabilities when measuring respiration or pulse. Simultaneously, this double peanut-shaped tapered structure design effectively reduces the impact of temperature on sensing performance by optimizing fiber mode interference effects, thereby achieving temperature-insensitive respiration and pulse signal monitoring.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, a dual peanut-shaped tapered fiber optic sensor comprises a first single-mode fiber, a multimode fiber, and a second single-mode fiber connected sequentially. The connection ends of the first single-mode fiber, the multimode fiber, and the second single-mode fiber are all spherical fusion splice surfaces formed by electrical discharge splicing. The spherical fusion splice surfaces of the first single-mode fiber and the multimode fiber form a first peanut-shaped structure through electrical discharge splicing, and the spherical fusion splice surfaces of the multimode fiber and the second single-mode fiber form a second peanut-shaped structure through electrical discharge splicing. The core of the multimode fiber is a tapered structure that is thin in the middle and wide at both ends.

[0008] Furthermore, the geometric diameter of the spherical welded surface is 173.25-173.33 μm.

[0009] Furthermore, the lengths of both the first and second peanut-shaped structures are 394.08-394.11 μm.

[0010] Furthermore, the length of the multimode optical fiber is 2.5-3cm.

[0011] Furthermore, the geometric diameter of the fiber core of the tapered structure is 83.52-83.58 μm.

[0012] Secondly, a method for fabricating a double peanut-shaped tapered fiber optic sensor includes the following steps:

[0013] S1: Cut one end of the single-mode fiber with the coating removed vertically to form a flat end face. After cleaning the flat end face, weld the flat end face to form a spherical fusion surface, and obtain a single-mode fiber with a spherical fusion surface at one end, namely the first spherical structure single-mode fiber.

[0014] Repeat the above process to obtain the second spherical single-mode optical fiber;

[0015] S2: The two ends of the multimode fiber with the coating removed are cut vertically to form flat end faces. After cleaning the flat end faces, the flat end faces at both ends of the multimode fiber are fused together to form spherical fusion surfaces, thus obtaining a multimode fiber with spherical fusion surfaces at both ends, i.e., a spherical structure multimode fiber.

[0016] S3: The spherical fusion splice surface of the first spherical single-mode fiber in step S1 is fused with the spherical fusion splice surface of one end of the spherical multimode fiber in step S2, so that the spherical fusion splice surface of the first spherical single-mode fiber and the spherical fusion splice surface of one end of the spherical multimode fiber are fused to form a first peanut-shaped structure.

[0017] S4: The spherical fusion splice surface at the other end of the spherical multimode fiber after fusion splicing in step S3 is fused with the spherical fusion splice surface of the second spherical single-mode fiber in step S1, so that the spherical fusion splice surface of the second spherical single-mode fiber and the spherical fusion splice surface at the other end of the spherical multimode fiber are fused to form a second peanut-shaped structure. The first spherical single-mode fiber, the second spherical single-mode fiber, and the spherical multimode fiber form a double peanut-shaped fiber optic sensor.

[0018] S5: Discharge and stretch the center position of the double peanut-shaped fiber optic sensor described in step S4 to form a tapered structure, thus obtaining a double peanut-shaped tapered fiber optic sensor.

[0019] Furthermore, the welding conditions described in step S1 or / and S2 are: discharge initiation intensity of 120 bits, discharge end intensity of 100 bits, and discharge time of 3000-3500 ms.

[0020] Furthermore, the geometric diameter of the spherical weld surface described in step S1 or / and S2 ranges from 173.25 to 173.33 μm.

[0021] Thirdly, the application of a double peanut-shaped tapered fiber optic sensor in medical and health monitoring, environmental monitoring, and early warning systems.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1. The fiber optic sensor of this invention can form MZI (Mach-Zehnder interference) through a double peanut-shaped tapered structure. Specifically, when light enters the first peanut-shaped region through optical coupling in a single-mode fiber, due to the abrupt change in the peanut-shaped structure of the fiber, the fundamental mode of the fiber is coupled into a higher-order mode, i.e., a portion of the light in the fiber core enters the cladding, while the remaining light propagates along the core of the multimode fiber. The two paths create an optical path difference. When the light wave propagates to the second peanut-shaped structure, the modes couple again and are ultimately output through the single-mode fiber to form MZI. When the curvature of the sensor undergoes slight deformation due to human respiration and pulse, the phase difference of the MZI changes, resulting in a change in the intensity of the Mach-Zehnder interference. Experiments have shown that when the length of the multimode fiber is 2.7 cm, the curvature changes from 0 to 1.138 m. -1 Within the range, the sensitivity is 13.803 dB / m. -1 This fiber optic sensor can achieve highly sensitive detection of respiratory and pulse signals.

[0024] 2. The fiber optic sensor of this invention, through its double peanut-shaped tapered structure design, can significantly reduce the impact of temperature on sensing performance. Tests have demonstrated that the temperature sensitivity of this fiber optic sensor is as low as 0.00211 μm. -1 / ℃ can eliminate the interference of ambient temperature on the measurement results.

[0025] 3. The preparation method of the present invention is simple and easy to operate. The double peanut-shaped tapered fiber optic sensor can be obtained by multiple fusion splicing and one stretching. At the same time, the raw materials are simple single-mode and multimode optical fibers, which reduces the manufacturing cost of the sensor and facilitates mass production.

[0026] In summary, the fiber optic sensor of the present invention, through its double peanut-shaped tapered structure design, makes the sensor highly sensitive to changes in curvature, with different sensitivities within different curvature ranges. At the same time, this double peanut-shaped tapered structure design can effectively reduce the influence of temperature on sensing performance. The fabrication method is simple, easy to operate, low in cost, and convenient for large-scale production. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the single-mode fiber end face being cut flat according to the present invention;

[0028] Figure 2 This is a schematic diagram of the multimode fiber end face being cut flat according to the present invention;

[0029] Figure 3 This is a schematic diagram of the spherical fusion splice surface at one end of the single-mode optical fiber of the present invention;

[0030] Figure 4 This is a schematic diagram of the spherical fusion splice surface at both ends of the multimode optical fiber of the present invention;

[0031] Figure 5 This is a schematic diagram of the double peanut-shaped optical fiber structure of the present invention;

[0032] Figure 6 This is a schematic diagram of the double peanut-shaped tapered optical fiber structure of the present invention;

[0033] Figure 7 This is a schematic diagram of the fiber transmission of the double peanut-shaped tapered optical fiber of the present invention;

[0034] Figure 8 This is a schematic diagram of the sensor system connection of the present invention;

[0035] Figure 9 This is a schematic diagram of the initial interference spectrum of the sensor of the present invention;

[0036] Figure 10 This is a schematic diagram of the sensor curvature measuring device of the present invention;

[0037] Figure 11 These are interference fringe spectra generated under different curvature conditions according to the present invention;

[0038] Figure 12 This is a curve showing the sensor curvature sensitivity fitting of the present invention;

[0039] Figure 13 This is a schematic diagram of the sensor temperature measuring device of the present invention;

[0040] Figure 14 The present invention generates interference fringe patterns at different temperatures;

[0041] Figure 15 This is the temperature sensitivity fitting curve of the present invention;

[0042] Figure 16 This is a schematic diagram of the pulse signal monitoring experimental device used in this invention;

[0043] Figure 17a This is the original pulse signal diagram of the oscilloscope used in this invention;

[0044] Figure 17b This is a signal diagram of the original pulse signal from the oscilloscope after filtering, as applied in this invention.

[0045] Figure 17c This is a signal diagram of the oscilloscope pulse filter signal after baseline drift removal, which is used in this invention.

[0046] Figure 18 This is a graph showing the pulse rate results of the application of this invention;

[0047] Figure 19 This is a schematic diagram of the respiratory signal monitoring experimental device used in this invention;

[0048] Figure 20aThis is the original breathing signal diagram from the oscilloscope used in this invention;

[0049] Figure 20b This is a signal diagram of the original respiratory signal from the oscilloscope after filtering, as used in this invention.

[0050] Figure 21 This is a graph showing the respiratory rate results of the application of this invention. Detailed Implementation

[0051] The following is in conjunction with the appendix Figure 1 To be continued Figure 21 The present invention will be further described in detail below:

[0052] In a first aspect, a dual peanut-shaped tapered fiber optic sensor comprises a first single-mode fiber, a multimode fiber, and a second single-mode fiber connected sequentially. The connection ends of each of the first single-mode fiber, the multimode fiber, and the second single-mode fiber are spherical fusion splice surfaces formed by electrical discharge splicing. The spherical fusion splice surfaces of the first single-mode fiber and the multimode fiber form a first peanut-shaped structure through electrical discharge splicing, and the spherical fusion splice surfaces of the multimode fiber and the second single-mode fiber form a second peanut-shaped structure through electrical discharge splicing. The core of the multimode fiber is a tapered structure that is thin in the middle and wide at both ends.

[0053] Furthermore, the geometric diameter of the spherical welded surface is 173.25-173.33 μm.

[0054] Furthermore, the lengths of both the first and second peanut-shaped structures are 394.08-394.11 μm.

[0055] Furthermore, the length of the multimode optical fiber is 2.5-3cm.

[0056] Furthermore, the geometric diameter of the thinnest part of the fiber core of the tapered structure is 83.52 mm.

[0057] -83.58μm.

[0058] Secondly, a method for fabricating a double peanut-shaped tapered optical fiber sensor involves fusing both ends of a multimode optical fiber to one end of each of two single-mode optical fibers to form a peanut shape, and then tapering the multimode optical fiber. The specific steps are as follows:

[0059] S1. Fabrication of spherical single-mode optical fiber: Figure 1As shown, firstly, the coating layer of the single-mode fiber is stripped off. Then, a fiber optic cleaver is used to vertically cut one end of the single-mode fiber to form a flat end face. After cleaning the flat end face with alcohol, the end of the single-mode fiber containing the flat end face is placed into a fiber optic fusion splicer for splicing. The flat end face of the single-mode fiber containing the flat end face is fused to form a spherical fusion surface, thus obtaining a single-mode fiber with one end containing a spherical fusion surface, which is the first spherical structure single-mode fiber.

[0060] Repeat the above process to obtain the following: Figure 3 The second spherical single-mode fiber shown;

[0061] S2. Fabrication of spherical multimode optical fibers: such as... Figure 2 As shown, firstly, the coating layer of the multimode fiber is stripped. Using a fiber optic cleaver, both ends of the stripped multimode fiber are vertically cut into flat end faces, forming multimode fibers with flat end faces at both ends. After cleaning the flat end faces with alcohol, the flat end faces at both ends of the multimode fiber are placed into a fiber optic fusion splicer for splicing to form spherical fusion surfaces. This process creates spherical fusion surfaces on the flat end faces at both ends of the multimode fiber, resulting in the desired fiber shape. Figure 4 The multimode fiber shown has spherical fusion splices at both ends, which is a spherical multimode fiber.

[0062] S3. Fusion splicing of the first spherical single-mode fiber, the spherical multimode fiber, and the second spherical single-mode fiber: Place the spherical fusion splice surface of the first spherical single-mode fiber from step S1 at one end of the fiber optic fusion splicer, and place the spherical fusion splice surface of one end of the spherical multimode fiber from step S2 at the other end of the fiber optic fusion splicer. Perform fusion splicing using the fiber optic fusion splicer's fusion program to fuse the spherical fusion splice surface of the first spherical single-mode fiber with the spherical fusion splice surface of one end of the spherical multimode fiber to form a first peanut-shaped structure.

[0063] S4: Place the spherical fusion splice surface of the other end of the spherical multimode fiber after fusion splicing in step S3 at one end of the fiber optic fusion splicer, and place the spherical fusion splice surface of the second spherical single-mode fiber in step S1 at the other end of the fiber optic fusion splicer. Perform fusion splicing using the fiber optic fusion splicer's fusion program, so that the spherical fusion splice surface of the second spherical single-mode fiber and the spherical fusion splice surface of the other end of the spherical multimode fiber are fused to form a second peanut-shaped structure. The first spherical single-mode fiber, the second spherical single-mode fiber, and the spherical multimode fiber form a double peanut-shaped fiber optic sensor. That is, the first spherical single-mode fiber and the second spherical single-mode fiber are fused with the spherical multimode fiber once to form a double peanut-shaped fiber optic sensor.

[0064] In step S3 and / or S4, the fiber optic fusion splicer fusion program is preferably set to a discharge start intensity of 100 bits, a discharge end intensity of 100 bits, and a discharge time of 2000 ms.

[0065] like Figure 5 As shown, the double peanut-shaped structure prepared by the optical fiber fusion splicer has high consistency in external dimensions and small structural differences, thereby reducing the error in the curvature experiment and ensuring the repeatability of subsequent experimental results.

[0066] S5. Fabrication of the tapered structure: Align the center position of the double peanut-shaped fiber optic sensor described in step S4 with the center position of the fiber optic fusion splicer and tighten it. Use the cleaning mode of the fusion splicer to discharge and stretch the double peanut-shaped fiber optic sensor to form a tapered structure. The cleaning discharge intensity bias is 180 bits, and the cleaning discharge time is 200 ms. During the discharge process, because the multimode fiber is in a taut state, the cleaning discharge reduces the diameter of the multimode fiber, resulting in the structure shown below. Figure 6 The fiber optic sensor with a double peanut-shaped tapered structure is shown.

[0067] Furthermore, the welding conditions described in step S1 or / and S2 are: discharge initiation intensity of 120 bits, discharge end intensity of 100 bits, and discharge time of 3000-3500 ms.

[0068] Furthermore, the geometric diameter of the spherical weld surface described in step S1 or / and S2 ranges from 173.25 to 173.33 μm.

[0069] Thirdly, a double peanut-shaped tapered fiber optic sensor is mainly used in multiple fields such as medical and health monitoring, vital sign tracking, environmental monitoring, and early warning systems. In particular, it can stably monitor the human pulse and respiratory rate when the ambient temperature changes significantly.

[0070] When light enters a single-mode fiber and reaches the first peanut-shaped structure, a portion of the light in the single-mode fiber core couples into the cladding of the multimode fiber. Simultaneously, the remaining light in the core propagates within the multimode fiber core, causing the light to propagate from a single core mode to two modes: cladding mode and core mode. Upon reaching the second peanut-shaped structure, some of the light propagating in the cladding re-enters the core. The core mode and cladding mode propagate through two paths with different refractive indices, satisfying the condition for two beams of light required for Mach-Zehnder interference. Finally, a Mach-Zehnder interference is formed by coupling in the second single-mode fiber. In the MZI structure, the interference intensity can be expressed as:

[0071] I = I1 + I2 + 2√I1I2COS(Δφ)

[0072] Where: I1 and I2 are the light intensities of the two interfering light paths, respectively, and Δφ is the phase difference, which is calculated using the following formula:

[0073]

[0074] Where: λ is the wavelength of the light source, L is the length of the optical fiber interference segment, and Δn eff This represents the effective refractive index difference between the two optical paths.

[0075] When the curvature of the sensor changes, the phase difference of the MZI changes, resulting in a change in the intensity of the Mach-Zehnder interference. When the sensor is attached to the surface of the human body, the subtle deformation of the surface caused by breathing and pulse will cause the optical fiber to bend slightly. Therefore, pulse and breathing can be detected by monitoring changes in transmission intensity.

[0076] Sensor Example:

[0077] This invention uses single-mode fiber (SMF) and multimode fiber (MMF) as the core materials for sensor fabrication. Example parameters: The core and cladding diameters of the SMF used in the experiment are 10 and 125 μm, respectively, and the core and cladding diameters of the MMF are 105 and 125 μm, respectively. Based on the characteristics of peanut-shaped tapered structure being easy to manufacture and highly repeatable, separate fabrication methods are adopted.

[0078] By designing the sensor structure and selecting the length of the multimode fiber, it is necessary to ensure that the length of the multimode fiber can generate a sufficient extinction ratio within the spectral range to achieve high sensitivity to curvature. By comparison, when the length of the multimode fiber is less than 2.5cm, the spectral extinction ratio is extremely small. When the length of the multimode fiber is greater than 3cm, the interference of the fiber in the sensor becomes complicated, affecting the clarity of the spectrum. Therefore, sensors made of multimode fibers with lengths of 2.5cm, 2.7cm, and 3cm were used to conduct curvature sensing experiments.

[0079] like Figure 8 As shown, the two ends of the fabricated double peanut-shaped tapered fiber optic sensor are connected to a demodulator, which is then connected to a computer. The computer controls the demodulator, displays the interference spectrum, and records experimental data. The spectrum displayed by the demodulator is as follows: Figure 9 As shown, the curvature and temperature sensitivity tests of the sensor were conducted, and the specific steps are as follows:

[0080] Step 1: As Figure 10 As shown, the fabricated double-peanut-shaped tapered fiber optic sensor is placed on a curvature variation platform and connected to a demodulator, which is connected to a computer. The initial distance between the two displacement platforms of the curvature variation platform is set to 21 cm. Both ends of the fiber optic sensor are fixed to the two displacement platforms, one as a fixed end and the other as a moving end. By controlling the displacement of the moving end, the sensor is bent, thereby achieving precise control and detection of curvature. By adjusting the displacement of the translation stage in 5 μm steps, the fiber optic sensor is bent, and the spectra at different curvatures are measured. Figure 11 As shown;

[0081] Step Two: As Figure 12 As shown, data fitting was performed on the obtained spectrum using the power corresponding to Dip2, revealing that the highest sensitivity of the double peanut-shaped tapered fiber optic sensor to curvature is 13.803 dB / m. -1 ;

[0082] Step 3: As Figure 13 As shown, the fabricated fiber optic sensor is connected to a demodulator, which is connected to a computer. The double peanut-shaped tapered structure is placed in a temperature chamber, and the temperature chamber is set to a temperature range of 20℃-50℃. The change of interference spectrum with temperature at different wavelengths is observed.

[0083] Step Four: As Figure 14 As shown, when the temperature inside the chamber gradually increases from 20℃ to 50℃, the spectral intensity hardly changes. Linear fitting of the Dip² values ​​of the interference spectra at different temperatures yields the following results. Figure 15 The fitted curve shown indicates that the temperature sensitivity of this fiber optic sensor is extremely low, at 0.00211 m. -1 / ℃, within the temperature range of 20℃-50℃, different temperatures will not affect the detection of pulse and respiration.

[0084] Experimental results show that when the length is 2.5cm, the curvature ranges from 0 to 4.962m. -1 Within this range, the sensitivity is 3.999 dB / m. -1 The curvature is 4.962-5.915m. -1 Within the range, the sensitivity is 3.550 dB / m. -1 When the length is 2.7cm, the curvature ranges from 0 to 1.138m. -1 Within the range, the sensitivity is 13.803 dB / m. -1 , 1.138-5.915m -1 Within the range, the sensitivity is 2.054 dB / m. -1 When the length is 3cm, the curvature ranges from 0 to 1.138m. -1 Within the range, the sensitivity is 7.886 dB / m. -1 The curvature is 1.138-5.915m. -1 Within the range, the sensitivity is 0.841 dB / m. -1 .

[0085] Comparative experiments were conducted to test the curvature response sensitivity of a sensor with only a peanut-shaped structure and no tapered section. The experimental results showed that, at a length of 2.7 cm, the sensor's curvature sensitivity was 0.209 dB / m. -1This sensitivity value is relatively small and cannot provide a sufficiently accurate response. Therefore, sensors that rely solely on a peanut-shaped structure are clearly insufficient in their sensitivity when detecting changes in curvature, and cannot meet the requirements for high-precision monitoring of curvature changes.

[0086] By comparing the spectra and sensitivity of the three sensors, it can be seen that the sensor with a length of 2.7cm has high sensitivity and better performance, and can achieve high sensitivity to bending.

[0087] Application Examples

[0088] Step 1: As Figure 16 As shown, a double peanut-shaped tapered fiber optic sensor is encapsulated on an elastic band and worn on the wrist. One end of the fiber optic sensor is connected to a laser, and the other end is connected to an oscilloscope.

[0089] Step Two: After storing the data from the oscilloscope in the computer, process the data using MATLAB. Figure 17a The raw data is first filtered to obtain Figure 17b Then Figure 17b Data after removing baseline drift was obtained Figure 17c The processed signal was then used to calculate the pulse rate as 68.6 beats per minute using peak value analysis. See details... Figure 18 As shown;

[0090] Step 3: As Figure 19 As shown, the fiber optic sensor is worn on the waist of the human body, and the data stored on the oscilloscope is then stored in the computer.

[0091] Step 4: Process the data using MATLAB to obtain the following results: Figure 20a The original respiratory signal diagram shown is then analyzed. Figure 20a Low-pass filtering is performed to remove noise and obtain Figure 20b The filtered respiratory signal diagram is shown below. Figure 21 As shown, the respiratory rate was calculated to be 21.9 breaths per minute using peak value calculation.

[0092] The working principle of this invention is as follows:

[0093] The transmission of light is as follows Figure 7As shown, the red arrows represent light in the fiber core, and the blue arrows represent light in the cladding. Light enters the first peanut-shaped region through optical coupling in a single-mode fiber. In this region, due to the abrupt change in fiber shape, the fundamental mode is coupled to a higher-order mode, and some light from the core enters the cladding; some light propagates along the core of the multimode fiber, and some propagates along the cladding, creating an optical path difference. When the light wave propagates to the second peanut-shaped structure, the modes couple again and are eventually output through the single-mode fiber, forming a Mach-Zehnder interferometer (MZI). When the curvature of the external environment changes, the optical path difference of the MZI changes, resulting in a change in the interference intensity. When the fiber is attached to the human body surface, the subtle deformation of the surface caused by breathing and pulse can cause the fiber to bend slightly. Therefore, changes in transmission intensity can be used to detect pulse and breathing.

Claims

1. A double peanut-shaped taper structure optical fiber sensor, comprising a first single-mode optical fiber, a multimode optical fiber, and a second single-mode optical fiber connected in sequence, characterized in that: The connecting ends of the first single-mode optical fiber, the multi-mode optical fiber, and the second single-mode optical fiber all have spherical fusion surfaces formed by discharge welding. The spherical fusion surfaces of the first single-mode optical fiber and the multi-mode optical fiber are formed into a first peanut-shaped structure by discharge welding. The respective spherical fusion surfaces of the multi-mode optical fiber and the second single-mode optical fiber are formed into a second peanut-shaped structure by discharge welding. The core of the multi-mode optical fiber is a tapered structure that is thin in the middle and wide at both ends.

2. The optical fiber sensor according to claim 1, characterized in that The geometric diameter of the spherical welding surface is 173.25-173.33 μm.

3. The optical fiber sensor according to claim 1, characterized in that: The lengths of the first peanut-shaped structure and the second peanut-shaped structure are both 394.08-394.11 μm.

4. The optical fiber sensor according to claim 1, characterized in that: The length of the multimode optical fiber is 2.5-3 cm.

5. The optical fiber sensor according to claim 1, characterized in that: The geometric diameter of the middle part of the core of the tapered structure is 83.52-83.58 μm.

6. A method for preparing a double peanut-shaped taper optical fiber sensor, characterized in that: The following steps are involved: S1: vertically cutting one end of a single-mode optical fiber stripped of a coating layer to form a flat end face, cleaning the flat end face, and then fusing the flat end face to form a spherical fusion surface, thereby obtaining a single-mode optical fiber having a spherical fusion surface at one end, i.e., a first spherical structure single-mode optical fiber; Repeat the above process to obtain a second spherical structure single-mode optical fiber; S2: vertically cutting the two ends of the multimode optical fiber from which the coating layer is stripped to form flat end faces, cleaning the flat end faces, and fusing the flat end faces at both ends of the multimode optical fiber to form spherical fusion surfaces, thereby obtaining a multimode optical fiber having spherical fusion surfaces at both ends, i.e., a spherical structure multimode optical fiber; S3: fusing the spherical fusion surface of the first spherical structure single-mode optical fiber in step S1 with the spherical fusion surface at one end of the spherical structure multimode optical fiber in step S2, so that the spherical fusion surface of the first spherical structure single-mode optical fiber and the spherical fusion surface at one end of the spherical structure multimode optical fiber are fused to form a first peanut-shaped structure; S4: fusing the spherical fusion surface at the other end of the spherical structure multimode optical fiber after fusion in step S3 with the spherical fusion surface of the second spherical structure single-mode optical fiber in step S1, so that the spherical fusion surface of the second spherical structure single-mode optical fiber and the spherical fusion surface at the other end of the spherical structure multimode optical fiber are fused to form a second peanut-shaped structure, and the first spherical structure single-mode optical fiber, the second spherical structure single-mode optical fiber and the spherical structure multimode optical fiber form a double peanut-shaped structure optical fiber sensor; S5: Discharge and stretch the center position of the double peanut-shaped optical fiber sensor in step S4 to form a tapered structure of the double peanut-shaped optical fiber sensor, thereby obtaining a double peanut-shaped tapered optical fiber sensor.

7. The preparation method according to claim 6, characterized in that: The welding conditions in step S1 and / or S2 are: the discharge starting intensity is 120 bits, the discharge ending intensity is 100 bits, and the discharge time is 3000-3500 ms.

8. The preparation method according to claim 6, characterized in that: The geometric diameter of the spherical welding surface in step S1 or / and S2 ranges from 173.25 to 173.33 μm.

9. An application of the double peanut-shaped taper structure optical fiber sensor according to claim 1 in medical health monitoring, environmental monitoring, and early warning systems.

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