A curvature sensor based on multi-core fiber tapering and its preparation method

Abstract

The present application proposes a curvature sensor based on multi-core fiber tapering and a preparation method. The curvature sensor includes: a first single-mode fiber region, a multi-core fiber region, a tapered micro-fiber region, and a second single-mode fiber region; the first single-mode fiber region includes: a first core, and the outside of the first core is coated with a first cladding, the second single-mode fiber region includes: a second core, and the outside of the second core is coated with a second cladding, the multi-core fiber region includes: multiple cores, and the multiple cores are configured such that one of the cores is used as the central core, and the remaining cores are arranged in a circumferential manner around the side wall of the central core, and the multi-core fiber region has a tapered structure that contracts from one end to the other along the axis direction of the central core, the first core is connected to the central core of the multi-core fiber region, and the side of the multi-core fiber region away from the first core is fusion spliced to the second single-mode fiber region through the tapered micro-fiber region. This curvature sensor is insensitive to temperature in the range of 30°C - 140°C and has extremely high sensitivity to curvature.

Description

Technical Field

[0001] This application relates to the technical field of sensors, and specifically relates to a curvature sensor based on multi-core fiber tapering and a preparation method thereof. Background Art

[0002] In recent years, the accurate measurement of the curvature of an object has played a crucial role in many applications such as medical devices, engineering structure monitoring, and aerospace engineering. Among many curvature sensors, fiber optic curvature sensors have been widely studied and applied due to their anti-electromagnetic interference, simple structure, and low cost. A variety of fiber optic curvature sensor devices have been proposed, such as Mach-Zehnder interferometers (MZI), Sagnac interferometers, fiber Bragg gratings (FBG), long-period fiber gratings (LPFG), etc. Among them, the sensor based on the Sagnac interferometer has a complex structure; the preparation of the sensors based on FBG and LPFG requires laser etching, with high preparation difficulty and cost; while the sensor based on MZI has attracted much attention due to its small size, simple preparation, and high sensitivity.

[0003] Currently, the MZI sensors used for curvature measurement are mainly of the Inline Mach-Zehnder Interferometer (IMZI) structure based on different types of fibers. IMZI concentrates the two transmission arms of the traditional MZI in one fiber, further reducing the volume and cost of the MZI and making its structure more compact and convenient for integration. In 2016, Jing Kong, Xiaowei Ouyang et al. proposed a highly sensitive directional bending sensor based on an eccentric fiber Mach-Zehnder modal interferometer, with a bending sensitivity of 13.49 nm / m -1 , however, the IMZI sensor based on the eccentric structure is usually sensitive not only to curvature but also to temperature or external refractive index at the same time, making it difficult to separate the signal responses from each other. In 2017, Meng-Zhu Zhang, Yu-Ming Ge et al. proposed an ultrasensitive curvature sensor based on a liquid crystal infiltrated fiber interferometer, with a maximum curvature sensitivity of up to 724.3 nm / m -1 , but it greatly increases the preparation difficulty and cost of the sensor. In 2018, Qi Wang and Yu Liu reported a curvature sensor based on the multimode fiber-seven core fiber-multimode fiber (MMF-SCF-MMF) structure, with a maximum curvature sensitivity of 41.46453 nm / m-1 In 2020, Rui Zhou, Xueguang Qiao et al. proposed a bending and tensile strain fiber optic sensor based on a laterally offset fusion seven-core fiber with the same structure, and its curvature sensitivity is 25.96 nm / m. -1 Although the sensor based on the MMF-SCF-MMF structure improves the curvature sensitivity of the sensor, its attenuation of light is extremely large, mostly between 15 - 25 dB, which is not conducive to practical applications.

[0004] For the MZI fabricated by the existing structure, the connection to the end face of the seven-core fiber is either through a fused ball or an eccentric fiber, which results in the following disadvantages of the fabricated device: (1) large attenuation of light; (2) difficulty in avoiding the problem of cross-sensitivity to external environments such as temperature and curvature; (3) complex structure.

[0005] Therefore, an improved curvature sensor based on the existing fiber tapering and its preparation method are needed. Summary of the Invention

[0006] To overcome the above-mentioned defect points, the purpose of this application is to provide a curvature sensor, the manufacturing method of which is simple and insensitive to temperature in a wide range, but has extremely high sensitivity to curvature.

[0007] To achieve the above purpose, the following technical solutions are adopted in this application:

[0008] A curvature sensor based on multi-core fiber tapering, characterized by successively including:

[0009] A first single-mode fiber region, a multi-core fiber region, a tapered micro-fiber region, and a second single-mode fiber region;

[0010] The first single-mode fiber region includes: a first core, and the first core is externally coated with a first cladding,

[0011] The second single-mode fiber region includes: a second core, and the second core is externally coated with a second cladding,

[0012] The multi-core fiber region includes: multiple cores, the multiple cores are configured with one of the cores as the central core, and the remaining cores are arranged in a circumferential pattern around the side wall of the central core, and the multi-core fiber region has a tapered structure that shrinks from one end to the other along the axis direction of the central core,

[0013] The first core is connected to the central core of the multi-core fiber region, and the side of the multi-core fiber region away from the first core is fused to the second single-mode fiber region through the tapered micro-fiber region.

[0014] Preferably, before the multi-core fiber is tapered, it is configured such that one of the cores serves as the central core, and the remaining cores are respectively parallel to the central core. After tapering, it forms a conical shape.

[0015] Preferably, the multi-core fiber region has a conical structure, and the diameter on the cone-head side is larger than the diameter of the cone-tail.

[0016] Preferably, the first core is connected to the central core from the cone-head side.

[0017] Preferably, the side of the second single-mode fiber region that is fused with the tapered micro-fiber region has a conical structure.

[0018] Preferably, the tapered micro-fiber region is configured with a cladding and no core.

[0019] Preferably, the outer diameter of the first cladding is larger than the diameter of the multi-core fiber arranged.

[0020] An embodiment of the present application provides a method for preparing a curvature sensor based on multi-core fiber tapering, characterized in that the method includes:

[0021] Place the first single-mode fiber, multi-core fiber, and second single-mode fiber in an optical fiber fusion splicer.

[0022] Align one end of the first core of the first single-mode fiber with the central core of the multi-core fiber, and align the second core of the second single-mode fiber with the other end of the central core of the multi-core fiber;

[0023] The alignment point of the first core and one end of the central core of the multi-core fiber is the first fusion point, and the alignment point of the second core of the second single-mode fiber and the other end of the central core of the multi-core fiber is the second fusion point. Use the optical fiber fusion splicer to perform fusion splicing to form an optical fiber fusion body.

[0024] Place the optical fiber fusion body on a hydrogen-oxygen tapering device, where the second fusion point is placed at the center of the tapering of the hydrogen-oxygen tapering machine. Adjust the hydrogen-oxygen ratio in the hydrogen-oxygen tapering machine to adjust the tapering speed. Through tapering, the multi-core fiber is tapered into a conical structure and a tapered micro-fiber region is formed between the cone-tail and the second single-mode fiber.

[0025] Beneficial effects

[0026] Compared with the prior art, for the curvature sensor proposed in the embodiment of the present application, this curvature sensor is based on the principle of a linear Mach-Zehnder interferometer (IMZI) and greatly reduces the optical attenuation in the sensor by tapering. The attenuation is between 8 - 12 dB, and its maximum curvature sensitivity can reach 174.02957 nm / m-1, greatly improving the sensitivity of the fiber curvature sensor. In addition, this sensor is insensitive to temperature in the range of 30°C - 140°C, which avoids the cross-sensitivity problem of temperature and curvature and is beneficial for practical applications. Description of the Drawings

[0027] Figure 1 This is the exposure splicing optical path diagram of the holographic lens in the embodiment of the present application.

[0028] Figure 2 This is the cross-sectional schematic diagram of the seven-core optical fiber in the embodiment of the present application.

[0029] Figure 3a This is the transmission spectrum of the IMZI in the embodiment of the present application. Figure 3b This is the schematic diagram of the FFT transformation of the transmission spectrum.

[0030] Figure 4 This is the schematic diagram of the temperature sensing experimental system in the embodiment of the present application.

[0031] Figure 5a This is the change of the transmission spectrum for curvature detection. Figure 5b This is the experimental and fitting curve of wavelength versus curvature.

[0032] Figure 6 This is the experimental and fitting curve of wavelength versus curvature of the curvature sensor based on multi-core fiber tapering with different lengths of seven-core optical fiber.

[0033] Figure 7 This is the experimental and fitting curve of wavelength versus curvature of the curvature sensor based on multi-core fiber tapering with different lengths of the tapered micro-fiber region.

[0034] Figure 8 This is the schematic diagram of the temperature sensing experimental system.

[0035] Figure 9a -c is the corresponding relationship between the wavelength value at the wave trough of the curvature sensor based on multi-core fiber tapering with different lengths of seven-core optical fiber and temperature. Detailed Description of the Invention

[0036] The above solution will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are for illustrative purposes only and do not limit the scope of the present application. The implementation conditions adopted in the embodiments can be further adjusted according to the conditions of specific manufacturers, and the implementation conditions not specified are usually those in conventional experiments.

[0037] The present application proposes a curvature sensor based on multi-core fiber tapering. This curvature sensor is based on the principle of a linear Mach-Zehnder interferometer (IMZI) and significantly reduces the optical attenuation in the sensor through the tapering method. The attenuation is between 8 - 12 dB, and its maximum curvature sensitivity can reach 174.02957 nm / m-1, greatly improving the sensitivity of the fiber curvature sensor. In addition, the sensor is insensitive to temperature in the range of 30°C - 140°C, which avoids the cross-sensitivity problem of temperature and curvature and is beneficial for practical applications.

[0038] Next, the curvature sensor based on multi-core fiber tapering proposed in this application will be described in conjunction with the accompanying drawings.

[0039] Embodiment 1:

[0040] As Figure 1 shown is a curvature sensor based on multi-core fiber tapering according to an embodiment of the present application.

[0041] The curvature sensor based on multi-core fiber tapering sequentially includes: a first single-mode fiber region 1, a multi-core fiber region 2, a tapered micro-fiber region 3, and a second single-mode fiber region 4.

[0042] The first single-mode fiber region is composed of a first core 5 and a first cladding 6 covering the outside thereof.

[0043] The second single-mode fiber region is composed of a second core 10 and a second cladding 11 covering the outside thereof.

[0044] The multi-core fiber region is composed of multiple cores and a cladding covering the outermost side of the multiple cores.

[0045] Among them, the arrangement of the multiple cores is as follows: one of the cores serves as the central core 7, and the remaining cores are evenly arranged around the circumferential wall of the central core.

[0046] The shape of the multi-core fiber region is a tapered structure that shrinks from one end to the other along the axis of its central core. The end with a larger diameter is the taper head 8, and the end with a smaller diameter is the taper tail 9. The first core of the first single-mode fiber region is connected to the central core of the multi-core fiber region from the taper head end. The taper tail end of the multi-core fiber region is fusion-spliced to the second single-mode fiber region through the tapered micro-fiber region. Before tapering, the remaining cores of the multiple cores are parallel to the central core.

[0047] The working mechanism of this curvature sensor:

[0048] Light is input from the second single-mode fiber region, and the light in the second core of the second single-mode fiber region is coupled into the multi-core fiber region through the tapered micro-fiber region. Since the diameter of the multi-core fiber in the multi-core fiber region is smaller than the mode field diameter, the light is no longer restricted to be transmitted in the central core of the multi-core fiber, but enters the cladding and the remaining cores for transmission and excites high-order modes, and finally is coupled into a single-mode fiber. Due to the different relative refractive indices of the fundamental mode and the high-order modes, the light transmission direction of the central core of the multi-core fiber remains unchanged during transmission. Since the shape of the multi-core fiber region shrinks from one end to the other along the axis of its central core to form a tapered structure, the light transmitted in the remaining cores deviates from the axis direction of the central core, and a corresponding optical path difference is generated between the light transmitted in the remaining cores and the light transmitted in the central core during the climbing process along the tapered surface of the tapered structure. As a result, interference occurs when the high-order mode is coupled back into the first single-mode fiber again.

[0049] Let the electric field strength of the incident light be:

[0050] E in = Aexp[i(ωt - β0n0x)] (1)

[0051] where A is the amplitude of the light wave; ω is the frequency; t is the time; β0 is the propagation constant; n0 is the effective refractive index of the fiber core; and x is the optical path. The total light intensity is:

[0052]

[0053] The light intensity of the high-order mode excited by the taper is:

[0054] I f = ξ f I (3)

[0055] where ξ f is the proportionality coefficient of the high-order mode light intensity to the input light intensity. When the high-order mode couples back to the fundamental mode, interference occurs, and the light intensity at this time is:

[0056]

[0057] where λ is the light wavelength, Δn eff is the difference in the effective refractive indices between the fundamental mode and the high-order mode, and L is the optical path.

[0058] In this method, a low-loss and high-contrast transmission filter is realized by directly fusing and tapering a single-mode and multi-core optical fiber. In this method: directly fusing a multi-core optical fiber and a single-mode optical fiber solves the problem of discontinuous connection of the optical fiber; in addition, after the multi-core optical fiber and the single-mode optical fiber are tapered, since the optical field leaks directly from the micro-fiber core to the cladding and then directly couples into the multi-core optical fiber after tapering, the optical field coupled into the multi-core optical fiber has much less loss compared to the structure of the prior art. Since the optical field forms interference in the first single-mode fiber region at the other end after being transmitted through the multi-core optical fiber, and since the energy entering the multi-core optical fiber is much stronger than that of other structures, the interference fringes have good contrast and are easy to perform sensing experiments.

[0059] Example 2

[0060] Next, the preparation of the above sensor is described. Taking a seven-core optical fiber as an example,

[0061] The preparation method of the curvature sensor based on multi-core fiber tapering includes the steps of:

[0062] First, place the first single-mode optical fiber, a seven-core optical fiber with a certain length (such as 2.1 cm long), and the second single-mode optical fiber in an optical fiber fusion splicer,

[0063] Align one end of the first core of the first single-mode fiber with the central core of the seven-core fiber, and align the other end of the second core of the second single-mode fiber with the central core of the seven-core fiber;

[0064] The alignment point of the first core with one end of the central core of the seven-core fiber is the first fusion joint.

[0065] The alignment point of the second core of the second single-mode fiber with the other end of the central core of the seven-core fiber is the second fusion joint, and use an optical fiber fusion splicer to perform fusion splicing to form an optical fiber fusion body;

[0066] Place the optical fiber fusion body on a hydrogen-oxygen taper machine, and place the second fusion joint at the center of the taper of the hydrogen-oxygen taper machine. Adjust the ratio of hydrogen to oxygen in the hydrogen-oxygen taper machine to adjust the taper speed. The seven-core fiber is tapered into a conical structure by tapering, and a tapered micro-fiber region is formed between the taper tail and the second single-mode fiber. In this embodiment, the flame sweep speed of the taper machine during tapering is 0.5 - 3.0 mm / s, and the moving speed of the fixed table during tapering is 0 - 0.5 mm / s; preferably, the flame sweep speed and the moving speed of the fixed table of the taper machine are 2.5 mm / s and 0.08 mm / s respectively. At this time, the length of the tapered micro-fiber region is 3.164 mm, and the diameter of the tapered micro-fiber region is 2 μm. In this embodiment,

[0067] The cross-section of the seven-core fiber is as Figure 2 shown, its cladding diameter is 150 μm, the core diameter is 8 μm, and the core pitch is 42 μm. At this time, the transmission spectrum of the spectrometer and the FFT transform of the transmission spectrum are as Figure 3a shown, showing strong interference in terms of wavelength, and the highest extinction ratio is 10.563 dB.

[0068] Figure 3b It is the FFT transform diagram of the transmission spectrum. It can be seen that the high-order mode is excited. By calculating, the coupling efficiency from the fundamental mode to the high-order mode is 41.88%. The curvature sensor prepared by this method is insensitive to temperature but has extremely high sensitivity to curvature. By combining the electric arc discharge method and the hydrogen-oxygen flame tapering method, a curvature sensor based on multi-core fiber tapering is fabricated. The curvature sensor based on multi-core fiber tapering belongs to a linear Mach-Zehnder interferometer with low loss. During the tapering process at the fusion joint of the multi-core fiber and the single-mode fiber (SMF), the light in each core of the multi-core fiber generates interference due to the optical path difference when coupling into the single-mode fiber, forming a comb-shaped peak. Using the curvature sensor based on multi-core fiber tapering to measure temperature and curvature, it is found that its highest sensitivity to temperature is 0.01771 nm / ℃ in the range of 30℃ - 140℃, and the curvature sensitivity can reach 174.02957 nm / m -1 , avoiding the problem of cross-influence between the two, and this is the highest curvature sensitivity among known multi-core fiber sensors.

[0069] Next, the performance of the curvature sensor will be described in combination with the test data.

[0070] When measuring the curvature change, the curvature sensor based on the tapered multi-core fiber is fixed on two moving platforms. The moving platform on the right is fixed, and the distance between the two moving platforms is adjusted by adjusting the micrometer on the left moving platform to achieve the change of the fiber curvature, as Figure 4 shown.

[0071] The calculation formula for the fiber curvature is:

[0072]

[0073] where \(l_0\) is the distance between the two moving platforms, \(R\) is the radius of curvature, \(x\) is the displacement of the left moving platform, and \(C\) is the curvature.

[0074] Figure 5a Shown is the change in the transmission spectrum of curvature detection when the length of the seven-core fiber is 2.1 cm. The 1547.8 nm valley is selected as the detection wavelength. When the bending curvature is 0.04702 m -1 the corresponding valley wavelength is 1543.18 nm. As the bending curvature increases, the valley will undergo a blue shift.

[0075] Figure 5b is the corresponding relationship between the wavelength value of the valley and the curvature. It can be seen from the curve that the wavelength and the curvature satisfy the relationship:

[0076] \(\lambda=-98.06988C + 1547.86764\)

[0077] The wavelength value and the curvature also have a linear relationship, \(R\) 2 = 0.9987. The measurement accuracy is 98.06988 nm / m -1 .

[0078] To verify the curvature sensitivity, the effects of the length of the seven-core fiber and the length of the tapered micro-fiber region on the curvature sensitivity were tested respectively.

[0079] First, the length of the seven-core fiber was changed to 1.0 cm, 1.5 cm, 2.1 cm, and 2.5 cm respectively, and the experiment was carried out with the length of the tapered micro-fiber region between 3.1 mm and 3.2 mm. The experimental results are as Figure 6 shown. It can be found that there is no obvious relationship between the length of the seven-core fiber and the sensitivity of the curvature sensor based on the tapered multi-core fiber. When the length of the seven-core fiber is 2.5 cm, the highest curvature sensitivity is 105.58707 nm / m -1Keep the length of the seven-core optical fiber unchanged at 2.1 cm, and the lengths of the tapered micro-fiber regions are 3.164 mm, 3.52 mm, and 3.862 mm respectively. The experimental results are as Figure 7 shown. As the length of the tapered micro-fiber region increases, the curvature sensitivity of the IMZI increases significantly. When the length of the tapered micro-fiber region is 3.862 mm, the curvature sensitivity is 174.02957 nm / m -1 . However, in actual preparation experiments, if the length of the tapered micro-fiber region is too short, no obvious interference can be generated. If the length of the tapered micro-fiber region is too long, the curvature sensor based on the tapered multi-core optical fiber is prone to breakage, which is not conducive to practical applications. Figure 6 Experimental and fitting curves of the wavelength and curvature of the curvature sensor based on the tapered multi-core optical fiber with different lengths of seven-core optical fibers.

[0080] Figure 7 are the experimental and fitting curves of the wavelength and curvature of the curvature sensor based on the tapered multi-core optical fiber with different lengths of the tapered micro-fiber region.

[0081] Figure 8 is the schematic diagram of the experimental system for temperature sensing. When measuring the temperature, a broadband light source of 1525 - 1575 nm is used as the experimental light source, and the environmental temperature is changed through an incubator, and the change of the transmission spectrum is monitored in real time by spectral analysis. Set the initial temperature to 140 °C, and gradually reduce the temperature to 30 °C, and record the transmission spectra corresponding to different temperatures.

[0082] Figure 9a-9c is the corresponding relationship between the wavelength value of the wave valley and the temperature of the curvature sensor based on the tapered multi-core optical fiber with different lengths of seven-core optical fibers. The lengths of the seven-core optical fibers are 1.1 cm, 1.5 cm, and 2.1 cm respectively, and the lengths of the tapered micro-fiber regions are all 3.1 mm - 3.2 mm. The wave valleys of different wavelengths are selected for detection. As the temperature decreases, the wavelength value corresponding to this wave valley will undergo a red shift. It can be found through experiments that the curvature sensor based on the tapered multi-core optical fiber is not sensitive to temperature. Under different lengths of seven-core optical fibers, its highest temperature sensitivity is only 0.01771 nm / °C.

[0083] Figure 9a Experimental and fitting curves of wavelength and temperature when the length of the seven-core optical fiber is 1.1 cm;

[0084] Figure 9b Experimental and fitting curves of wavelength and temperature when the length of the seven-core optical fiber is 1.5 cm;

[0085] Figure 9c Experimental and fitting curves of wavelength and temperature when the length of the seven-core optical fiber is 2.1 cm;

[0086] It is found through experiments on curvature and temperature that the curvature sensor based on tapered multi-core fiber is insensitive to temperature in the range of 30°C - 140°C, but has extremely high sensitivity to curvature. Moreover, by increasing the length of the tapered region, the curvature sensitivity of the curvature sensor based on tapered multi-core fiber can be further improved. When the length of the tapered micro-fiber region is 3.862 mm, the curvature sensitivity can reach 174.02957 nm / °C. And due to its extremely low temperature sensitivity, the problem of cross-influence between temperature and curvature in practical applications is well avoided.

[0087] The above embodiments are only for illustrating the technical concept and characteristics of the present application, and their purpose is to enable those who are familiar with this technology to understand the content of the present application and implement it accordingly, and cannot be used to limit the protection scope of the present application. Any equivalent transformation or modification made in accordance with the spirit of the present application should be covered within the protection scope of the present application.

Claims

1. A curvature sensor based on the taper of a multi-core optical fiber, characterized in that Including in order: A first single-mode optical fiber area, a multi-core optical fiber area, a tapered micro-optical fiber area, and a second single-mode optical fiber area; The first single-mode optical fiber region comprises: a first fiber core, and the first fiber core is coated with a first cladding. The second single-mode optical fiber region comprises: a second fiber core, and the second fiber core is coated with a second cladding. The multi-core optical fiber area comprises: a plurality of fiber cores, wherein the plurality of fiber cores are configured to have one of the fiber cores as a central fiber core, and the remaining fiber cores are arranged around the circumference of the side wall of the central fiber core, and the multi-core optical fiber area is a tapered structure that contracts from one end to the other end along the axis direction of the central fiber core, The first fiber core is connected to the central fiber core of the multi-core fiber zone, and the side of the multi-core fiber zone away from the first fiber core is fused with the second single-mode fiber zone through a tapered micro-fiber zone; The tapered micro-fiber region is provided with a cladding but no core.

2. The curvature sensor based on multi-core optical fiber taper according to claim 1, characterized in that: Before tapering, the plurality of fiber cores are arranged so that one of the fiber cores is used as a central fiber core, and the remaining fiber cores are parallel to the central fiber core.

3. The curvature sensor based on the taper of a multi-core optical fiber according to claim 1, characterized in that, The multi-core optical fiber area is in a cone-shaped structure, and the diameter of the cone head side is larger than the diameter of the cone tail side.

4. The curvature sensor based on multi-core optical fiber taper according to claim 3, characterized in that: The first core is connected to the central core from the cone head side.

5. The curvature sensor based on multi-core optical fiber taper according to claim 1, characterized in that: The side of the second single-mode optical fiber zone fused with the tapered micro-optical fiber zone presents a tapered structure.

6. The curvature sensor based on multi-core optical fiber taper according to claim 1, characterized in that: The outer diameter of the first cladding is larger than the diameter of the multiple fiber cores.

7. A preparation method of a curvature sensor based on multi-core fiber tapering, characterized in that, The method comprises: Place the first single-mode optical fiber, the multi-core optical fiber, and the second single-mode optical fiber in an optical fiber fusion splicer. Aligning the first fiber core of the first single-mode optical fiber with one end of the central fiber core of the multi-core optical fiber, and aligning the second fiber core of the second single-mode optical fiber with the other end of the central fiber core of the multi-core optical fiber; The first fusion point is where the first fiber core is aligned with one end of the central fiber core of the multi-core optical fiber. The second fiber core of the second single-mode optical fiber is aligned with the other end of the central fiber core of the multi-core optical fiber as a second fusion point, and a fiber fusion splicer is used to perform fusion splicing to form a fiber fusion body; The optical fiber fusion body is placed on a hydrogen-oxygen taper pulling device, wherein the second fusion point is placed at the taper center of the hydrogen-oxygen taper pulling machine, and the ratio of hydrogen and oxygen in the hydrogen-oxygen taper pulling machine is adjusted to adjust the taper pulling speed. The multi-core optical fiber is pulled into a tapered structure through taper pulling and a taper micro-fiber area is formed between the taper tail and the second single-mode light, wherein the taper micro-fiber area is provided with a cladding but no core.

8. The preparation method of the curvature sensor based on multi-core fiber tapering according to claim 7, characterized in that, When drawing the taper, the flame sweeping speed of the taper drawing machine is 0.5 to 3.0 mm / s.

9. The preparation method of the curvature sensor based on multi-core fiber tapering according to claim 7, characterized in that, The moving speed of the fixed table during taper drawing is 0 to 0.5 mm / s.

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