A temperature and curvature sensor based on seven-core fiber and a method for manufacturing the same

Abstract

This invention provides a temperature and curvature sensor based on a seven-core optical fiber and its fabrication method, belonging to the field of optical fiber sensing technology. It solves the problem of low temperature sensitivity in existing seven-core optical fiber sensors. The technical solution is as follows: the sensor is composed of a broadband light source, a first single-mode optical fiber, a conical region, a seven-core optical fiber, a first spherical structure, a second spherical structure, a second single-mode optical fiber, and a spectrometer connected sequentially. The fabrication method includes the following steps: S1, fusing the first single-mode optical fiber and the seven-core optical fiber; S2, arc-discharging the right end of the seven-core optical fiber to form a spherical structure to obtain the first spherical structure; S3, arc-discharging the end of the second single-mode optical fiber to obtain the second spherical structure; S4, fusing the first spherical structure and the second spherical structure to obtain a peanut-shaped structure; S5, tapering the first fusion point of the single-mode optical fiber fused with the seven-core optical fiber to obtain the sensor. The beneficial effects of this invention are: the curvature sensor of this invention has extremely high sensitivity to both temperature and curvature.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and in particular to a temperature and curvature sensor based on a seven-core optical fiber and its fabrication method. Background Technology

[0002] Fiber optic sensors, due to their simple structure, high sensitivity, and resistance to electromagnetic interference, are widely used in environmental monitoring, biomedicine, and aerospace fields to measure various physical parameters, such as strain, temperature, bending, displacement, and pressure. Currently, fiber optic sensor structures mainly fall into two categories: grating-type structures and interferometric structures. Grating-type fiber optic sensors, including long-period fiber gratings (LPFGs) and tilted FBGs (FBGs), offer advantages such as miniaturization and high precision. However, because the grating structure needs to be etched onto the fiber, they suffer from high manufacturing process requirements and high production costs.

[0003] Interferometer sensors, such as the Sagnac ring, Michelson interferometer, and Mach-Zehnder interferometer (MZI), have attracted widespread interest from researchers due to their simple fabrication process and large measurement range. Among these, the MZI has garnered significant attention due to its high sensitivity and structural stability.

[0004] To improve the sensitivity of fiber optic sensors, modifying the MZI structure is an effective method, such as using top-conical, side-offset, peanut-shaped, or spherical structures. The peanut-shaped structure is particularly robust and can effectively excite core and cladding modes, achieving coupling between higher-order modes, making it an effective way to achieve high-sensitivity sensors. Compared to conventional optical fibers, microfibers, due to their higher evanescent field, can effectively detect external environmental parameters, becoming another effective method to improve sensor sensitivity.

[0005] To date, there has been relatively little research on the temperature sensing characteristics of seven-core optical fibers. Furthermore, the fusion splicing of direct multimode fiber / coreless fiber / hollow fiber with seven-core fiber limits the excitation of higher-order modes and results in a short contact distance between higher-order modes and the external environment, which affects the improvement of fiber temperature sensitivity and hinders the application of seven-core optical fibers in temperature sensors.

[0006] How to solve the above-mentioned technical problems is the challenge facing this invention. Summary of the Invention

[0007] The purpose of this invention is to provide a temperature and curvature sensor based on a seven-core optical fiber and its fabrication method. This high-sensitivity temperature sensor is based on a seven-core optical fiber. One end of the seven-core fiber is connected to a single-mode fiber via a fused taper to achieve low-loss optical coupling between single and multiple cores. The other end of the seven-core fiber is fused into a spherical shape and fused with another spherical single-mode fiber to form a peanut-like structure. Compared with the traditional peanut structure, this novel peanut structure, with its two spheres composed of two different types of optical fibers, exhibits better intermodal interference capability. Combined with the strong evanescent field characteristic of the taper fiber itself, it achieves high-sensitivity temperature and curvature sensing characteristics, overcoming the drawback of the seven-core fiber's insensitivity to temperature. This sensor has a simple structure, is easy to manufacture, has low cost, and possesses extremely high temperature sensitivity, making it easy to fabricate.

[0008] This invention is achieved through the following measures: a temperature and curvature sensor based on a seven-core optical fiber and its fabrication method, wherein the sensor is based on a tapered single-mode fiber-tapered seven-core optical fiber-double sphere-single-mode fiber structure; and is composed of a broadband light source, a first single-mode fiber, a tapered region, a seven-core optical fiber, a first spherical structure, a second spherical structure, a second single-mode fiber, and a spectrometer connected sequentially;

[0009] In this configuration, the first single-mode fiber serves as the input end of the sensor. One end of the first single-mode fiber is connected to a broadband light source via an FC / APC fiber optic connector. The two ends of the conical region are respectively connected to the other end of the first single-mode fiber and one end of a seven-core fiber. The other end of the seven-core fiber is a first spherical structure. A second spherical structure is connected to one end of the first spherical structure. The other end of the second spherical structure is connected to one end of a second single-mode fiber, which serves as the output end. The other end of the second single-mode fiber is connected to the signal interface of the spectrometer via an FC / APC fiber optic connector.

[0010] Furthermore, the first single-mode fiber and the second single-mode fiber are ordinary standard single-mode fibers, such as single-mode fiber G.652, single-mode fiber G.654, single-mode fiber G.655 or single-mode fiber G.656; the core and cladding refractive indices are 1.4682 and 1.4629, respectively, and the cladding and core diameters are 125 μm and 8.2 μm, respectively.

[0011] Furthermore, the conical region includes a tapered region, a widening region, and a conical waist portion; the fiber diameter in the tapered region gradually decreases, the fiber diameter in the widening region gradually increases, and the fiber diameter in the conical waist portion is the smallest and remains constant.

[0012] The tapered region is formed by splicing seven-core optical fibers and single-mode optical fibers and then tapering them. The length of the tapered region after tapering is 2 mm-40 mm.

[0013] Furthermore, the first spherical structure has a major radius of 138.9 μm and a minor radius of 110 μm, wherein the size and shape of the sphere can be precisely adjusted and controlled by adjusting the amount and number of discharges.

[0014] Furthermore, the second spherical structure has a long radius of 110 μm and a short radius of 98 μm, and the size and shape of the sphere can be precisely adjusted and controlled by adjusting the discharge intensity and the number of discharges.

[0015] Furthermore, the first single-mode fiber is connected to a broadband light source, and the second single-mode fiber is connected to a spectrometer with a resolution of 0.02 nm.

[0016] To better achieve the above-mentioned objectives, this invention also provides a method for fabricating a temperature and curvature sensor based on a seven-core optical fiber with a tapered peanut-shaped structure. The fabrication process involves using a fiber optic fusion splicer and an oxyhydrogen flame tapering machine to obtain the structure, specifically including the following steps:

[0017] S1. Connect one end of the first single-mode fiber to the broadband light source through the FC / APC fiber connector. Cut the other end of the first single-mode fiber and the seven-core fiber flat and place them on the fiber fusion splicer to fuse. The fusion point is the first fusion point. The length of the seven-core fiber is 2cm.

[0018] S2. Use a fusion splicer to fuse the other end of the seven-core optical fiber into a sphere as the first spherical structure. Perform multiple arc discharges on the right end of the seven-core optical fiber. The long radius of the first spherical structure is 138.9μm and the short radius is 110μm. The diameter of the first spherical structure is controlled and adjusted by the discharge intensity and number of discharges of the fusion splicer. The first spherical structure is repeatable and its size and shape can be adjusted.

[0019] S3. The second single-mode fiber is connected to the spectrometer via an FC / APC fiber optic connector. The spectrometer uses the same method as in step S2 to fuse a second spherical structure to the other end of the second single-mode fiber. The shape and size of the second spherical structure can also be adjusted.

[0020] S4. On the welding machine, the first spherical structure and the second spherical structure are brought close together and welded together by electric discharge to obtain a peanut-shaped structure. The welding of the two spherical structures can be either a concentric connection or an eccentric connection.

[0021] S5. Place the single-mode fiber fusion spliced ​​with a seven-core fiber structure obtained in step S1 stably on the hydrogen-oxygen flame tapering machine, align the tapering machine with the first splice point, and during tapering, the flame scanning range covers the point. After tapering, this structure is obtained.

[0022] Furthermore, in step S2, the fusion splicer fuses one end of the seven-core optical fiber into a sphere using a manual fusion splicing mode, with a discharge intensity range of 130-150 and a discharge time of 750-950 ms.

[0023] Furthermore, at 1 Pa and 25 °C, the flow rates of oxygen and hydrogen on the tapered machine are 8.0 mL / min and 110 mL / min, respectively.

[0024] The flame scanning speed and clamping speed of the tapering machine are 2.5 mm / s and 0.08 mm / s, respectively, and the flame scanning length is 2 mm. The waist diameter of the tapered fiber is controlled by changing the tapered length. When a clear comb-like peak is observed, the tapering stops. After tapering, the expected spectrum is obtained. The length of the tapered region after tapering is 4.8789 mm.

[0025] Furthermore, the tapered region includes a tapered region, a expanding region, and a tapered waist. In the tapered region, the fiber diameter gradually decreases, while in the expanding region it gradually increases. The fiber diameter is smallest and remains constant in the tapered waist. As the molten portion of the fiber gradually thins, the rate of thinning can be determined by the volumetric flow rates of hydrogen and oxygen. Therefore, the dimensions of the tapered section can be precisely controlled by setting these parameters, enabling repeated fabrication of this structure. After multiple re-fabrications, it is believed that this structure is not only simple to fabricate and easy to operate, but also easy to repeat.

[0026] like Figure 3 The diagram shows the curvature measurement device for the sensor of this invention. The sensor is fixed to two translation stages using a micrometer. Rotating the micrometer on the translation stages changes the distance between the two stages, thus indirectly changing the curvature by altering the radius of curvature. Figure 4 As shown in (a), when the curvature changes, the position of the trough on the spectrometer shifts to the left, and the wavelength (λ) and curvature (C) show a linear relationship, as... Figure 4 As shown in (b), the curvature sensitivity of the trough is as high as -93.34 nm / m. -1 Meanwhile, it can be seen that the fringe period (FSR) ranges from 19 to 20 nm, which is beneficial for curvature measurement.

[0027] like Figure 5 The diagram shown is of the temperature measurement device for the sensor of this invention. By changing the temperature of the constant temperature chamber, a shift diagram of the spectrum as a function of temperature (T) is obtained, as shown below. Figure 6 As shown in (a), within a very small temperature range, the spectral shift is significant. Observing the position of the trough on the spectrometer, the wavelength (λ) and temperature (T) show a linear relationship, as shown in (a). Figure 6 As shown in (b), the temperature sensitivity is -836.6 pm / ℃, which is the highest sensitivity temperature and curvature sensor we know of among seven-core fiber optic sensors.

[0028] The optical propagation sequence of the sensor of this invention is as follows:

[0029] The incident light from broadband light source 1 passes through the first single-mode fiber. As the diameter of the single-mode fiber gradually decreases compared to the mode field diameter, light leaks from the core into the cladding. Through the conical region, the light can naturally couple into all seven cores of the seven-core fiber. When the light passes through the first spherical structure from the core of the seven-core fiber, some light leaks into the cladding to excite higher-order modes, while the rest continues to propagate in the fundamental mode. When the light reaches the junction of the first and second spherical structures, the two modes couple and then split. The light is injected into the core of the second single-mode fiber. Throughout this process, due to the optical path difference between the fundamental and higher-order modes, the phase-matching condition is met, thus generating an interference spectrum on the spectrometer. The curvature and temperature are measured by the shift in the wavelength of the interference valleys in the spectrum.

[0030] The working principle of this invention is as follows: Incident light enters the conical region through the first single-mode fiber. Due to the small diameter of the conical region, higher-order modes are excited. Subsequently, due to the superfiber connection between the first single-mode fiber and the seven-core fiber, the light is coupled into the seven cores of the seven-core fiber with low loss. After the incident light propagates 2 cm in the seven-core fiber, the first spherical structure acts as a beam combiner to help the incident light enter. Then, through the beam splitting effect of the second spherical structure, it is coupled back into the second single-mode fiber and transmitted to the spectrometer to obtain the transmission spectrum. During the transmission of the incident light, the fundamental mode and the cladding mode generate an optical path difference due to the difference in refractive index, thus producing a Mach-Zehnder interference spectrum on the spectrometer. Changes in temperature and curvature will cause changes in the effective refractive index difference between the fundamental mode and the cladding mode, resulting in a wavelength shift in the spectrum. Temperature and curvature are measured by detecting the wavelength.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] 1. This invention is based on a tapered single-mode fiber-tapered seven-core fiber-double sphere-single-fiber structure, combining the characteristics of tapered and double spheres to achieve a significant improvement in temperature sensitivity, further enhancing the practicality of temperature and curvature sensors. It is not only simple to manufacture but also inexpensive to use. It only requires simple discharge fusion splicing with a fiber optic fusion splicer and simple tapering with a tapering machine. The tapered and double sphere structures are not only simple in structure and easy to manufacture, but also functionally can replace expensive and complex optical devices and have similar effects. It has great potential for the widespread use of fiber optic temperature and curvature sensors.

[0033] 2. Compared to traditional single-mode-seven-core-single-mode fiber, the peanut-like structure of this invention is composed of two different fiber ends, a seven-core fiber and a single-mode fiber, fused together into a spherical shape. Due to the multi-core distribution characteristics of the seven-core fiber's cross-section, fusing its ends into a sphere makes it easier to excite the fundamental mode light to higher-order modes compared to a single-mode fiber with only one core in its cross-section, resulting in higher sensor sensitivity. Furthermore, by changing the fusion method of the two spherical structures—either concentric or eccentric fusion—the peanut-like structure can be adjusted, thereby regulating the sensor's sensitivity. Because this sensor structure excites more higher-order modes, these modes exhibit extremely high sensitivity to temperature and curvature.

[0034] 3. Compared with the traditional single-mode-double-sphere-single-mode fiber tapered structure, in the sensor of this invention, the single-mode fiber is first connected to the seven-core fiber tapered structure, which can first excite some higher-order modes. Then, by fusing the seven-core fiber into a double-sphere tapered structure, the higher-order modes are further excited, thereby achieving a qualitative improvement in temperature sensitivity and obtaining the highest temperature sensitivity.

[0035] 4. The sensor output signal of the present invention contains interference peaks formed by mode interference. The sensitivity is detected by the change of wavelength of interference valley with temperature and curvature. It is highly sensitive to curvature and temperature, and has good application prospects in the fields of biological detection and environmental monitoring.

[0036] 5. The dimensions of the tapered sensor of the present invention can be precisely controlled and adjusted by setting these parameters, enabling repeated fabrication and customized preparation of this structure. At the same time, the position of the center point of the tapered region can also be adjusted by placing the single-mode fiber and the fusion splice point of the seven-core fiber. After repeated fabrication in the experiment, the structure is not only simple to prepare and easy to operate, but also easy to repeat.

[0037] 6. This invention enhances sensitivity by stimulating higher-order modes with extremely high temperature and curvature sensitivity. It has advantages such as low cost, ease of fabrication, and small size, greatly improving the practicality of fiber optic temperature and curvature sensors. It has promising application prospects in environmental monitoring, biochemistry, medicine, and aerospace. Attached Figure Description

[0038] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0039] Figure 1 This is a schematic diagram of the sensor structure of the present invention.

[0040] Figure 2(a) is a schematic diagram of the peanut-shaped structure with the core connected, and (b) is a schematic diagram of the peanut-shaped structure with the eccentric core connected.

[0041] Figure 3 This is a schematic diagram of the apparatus used by the sensor of the present invention to measure curvature.

[0042] Figure 4 In the diagram, (a) is a wavelength (λ) shift plot as curvature (C) changes, and (b) is a fitted curve of curvature (C) and wavelength (λ) obtained for the trough in (a).

[0043] Figure 5 This is a schematic diagram of the apparatus used for temperature curvature testing of the sensor of the present invention.

[0044] Figure 6 In the diagram, (a) shows the wavelength shift as a function of temperature, and (b) shows the fitted curves of temperature and wavelength obtained for the troughs in (a).

[0045] Figure 7 This is a flowchart illustrating the fabrication process of the curvature sensor of the present invention.

[0046] The attached figures are labeled as follows: 1. Broadband light source; 2. First single-mode fiber; 3. Conical region; 3-6 (conical region, seven-core fiber, first spherical structure, second spherical structure); 4. Seven-core fiber; 5. First spherical structure; 6. Second spherical structure; 7. Second single-mode fiber; 8. Spectrometer; 9. Rotary translation stage; 10. Micrometer; 11. Temperature chamber. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. Of course, the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0048] Example 1

[0049] See Figures 1 to 7 The technical solution provided in this embodiment is a temperature and curvature sensor based on a seven-core optical fiber. The sensor is based on a tapered single-mode fiber-tapered seven-core optical fiber-double sphere-single-mode optical fiber structure; it is composed of a broadband light source 1, a first single-mode optical fiber 2, a tapered region 3, a seven-core optical fiber 4, a first spherical structure 5, a second spherical structure 6, a second single-mode optical fiber 7, and a spectrometer 8 connected in sequence.

[0050] The first single-mode fiber 2 is the input end of the sensor. One end of the first single-mode fiber 2 is connected to the broadband light source 1 through an FC / APC fiber optic connector. The two ends of the cone region 3 are connected to the first single-mode fiber 2 and the seven-core fiber 4, respectively. The other end of the seven-core fiber 4 is the first spherical structure 5. The second spherical structure 6 is connected to the first spherical structure 5. The other end of the second spherical structure 6 is connected to the second single-mode fiber 7, which serves as the output end. The second single-mode fiber 7 is connected to the signal interface of the spectrometer 8 through an FC / APC fiber optic connector.

[0051] Furthermore, the first single-mode fiber 2 and the second single-mode fiber 7 are ordinary standard single-mode fibers with core and cladding refractive indices of 1.4682 and 1.4629, respectively, and cladding and core diameters of 125 μm and 8.2 μm, respectively.

[0052] Furthermore, the cone region 3 includes a tapered region, a expanding region, and a cone waist portion; the fiber diameter in the tapered region gradually decreases, the fiber diameter in the expanding region gradually increases, and the fiber diameter in the cone waist portion is the smallest and remains constant.

[0053] The tapered region 3 is formed by splicing seven-core optical fiber 4 and first single-mode optical fiber 2 and then tapering it. The length of the tapered region after tapering is 4.8789 mm.

[0054] Furthermore, the first spherical structure 5 has a major radius of 138.9 μm and a minor radius of 110 μm.

[0055] Furthermore, the second spherical structure 6 has a major radius of 110 μm and a minor radius of 98 μm.

[0056] Furthermore, the first single-mode fiber 2 is connected to a broadband light source 1, and the second single-mode fiber 7 is connected to a spectrometer 8, the spectrometer 8 having a resolution of 0.02nm.

[0057] To better achieve the above-mentioned objectives, this embodiment also provides a temperature and curvature sensor based on a seven-core optical fiber and its fabrication method. The fabrication process utilizes a combination of an optical fiber fusion splicer (FURUKAWA S178C) and an oxyhydrogen flame taper to obtain this structure, specifically including the following steps:

[0058] S1. Connect one end of the first single-mode fiber 2 to the broadband light source 1 through the FC / APC fiber connector. Cut the other end of the first single-mode fiber 2 and the seven-core fiber 4 flat and place them on the fiber fusion splicer for splicing. The splice point is the first splice point. The length of the seven-core fiber is 2 cm.

[0059] S2. Use a fusion splicer to fuse the other end of the seven-core optical fiber 4 into a sphere, which is the first spherical structure 5. Perform multiple arc discharges on the right end of the seven-core optical fiber 4. The long radius of the first spherical structure 5 is 138.9 μm and the short radius is 110 μm. The diameter of the first spherical structure 5 is controlled by the discharge intensity and the number of discharges of the fusion splicer. The first spherical structure 5 is repeatable.

[0060] S3. The second single-mode fiber 7 is connected to the spectrometer 8 via an FC / APC fiber optic connector. The spectrometer 8 uses the same method as in step S2 to fuse the second spherical structure 6 to the other end of the second single-mode fiber.

[0061] S4. On the welding machine, bring the first spherical structure 5 and the second spherical structure 6 close together and weld them together by electric discharge to obtain a peanut-shaped structure;

[0062] S5. Place the structure obtained in step S1, which is fused with the first single-mode fiber 2 and the seven-core fiber 4, stably on the hydrogen-oxygen flame tapering machine, align the tapering machine with the first fusion point, and when tapering, cover the point with the flame scanning range. After tapering, this structure is obtained.

[0063] Furthermore, in step S2, the fusion splicer fuses one end of the seven-core optical fiber 4 into a sphere using a manual fusion splicing mode, with a discharge intensity range of 130-150 and a discharge time of 750-950 ms.

[0064] Furthermore, at 1 Pa and 25 °C, the flow rates of oxygen and hydrogen on the tapered machine were 8.0 mL / min and 110 mL / min, respectively.

[0065] The flame scanning speed and clamping speed of the tapering machine are 2.5 mm / s and 0.08 mm / s, respectively. The flame scanning length is 2 mm. The waist diameter of the tapered fiber is controlled by changing the tapered length. When a clear comb-like peak is observed, the tapering stops. After tapering, the expected spectrum is obtained. The length of the tapered region after tapering is 4.8789 mm.

[0066] Furthermore, the tapered region 3 includes a tapered region, a expanding region, and a tapered waist. In the tapered region, the fiber diameter gradually decreases, while in the expanding region it gradually increases. The fiber diameter is smallest and remains constant in the tapered waist. As the molten portion of the fiber gradually thins, the rate of thinning can be determined by the volumetric flow rates of hydrogen and oxygen. Therefore, the dimensions of the tapered section can be precisely controlled by setting these parameters, enabling repeated fabrication of this structure. After multiple re-fabrications, it is believed that this structure is not only simple to fabricate and easy to operate, but also easy to repeat.

[0067] like Figure 3The diagram shows the curvature measurement device for the sensor in this embodiment. The sensor is fixed to two translation stages 9 using a micrometer 10. Rotating the micrometer 10 on the translation stages changes the distance between the two stages 9, thus indirectly changing the curvature by altering the radius of curvature. Figure 4 As shown in (a), when the curvature changes, the position of the trough on the spectrometer shifts to the left, and the wavelength (λ) and curvature (C) have a linear relationship, as shown in (a). Figure 4 As shown in (b), the curvature sensitivity of the trough is as high as -93.34 nm / m. -1 Meanwhile, it can be seen that the fringe period (FSR) ranges from 19 to 20 nm, which is beneficial for curvature measurement.

[0068] like Figure 5 The diagram shown is of the temperature measurement device for the sensor in this embodiment. By changing the temperature of the constant temperature chamber 11, a shift diagram of the spectrum as a function of temperature (T) is obtained, as shown below. Figure 6 As shown in (a), within a very small temperature range, the spectral shift is significant. Observing the position of the trough on the spectrometer, the wavelength (λ) and temperature (T) show a linear relationship, as shown in (a). Figure 6 As shown in (b), the temperature sensitivity is -836.6 pm / ℃, which is the highest sensitivity temperature and curvature sensor we know of among seven-core fiber optic sensors.

[0069] In this embodiment, the optical propagation sequence of the sensor is as follows:

[0070] The incident light output from the broadband light source 1 passes through the first single-mode fiber 2. As the diameter of the single-mode fiber gradually decreases compared to the mode field diameter, the light leaks from the core into the cladding. Through the conical region 3, the light can naturally couple into all seven cores of the seven-core fiber 4. When the light passes from the core of the seven-core fiber 4 through the first spherical structure 5, some light leaks into the cladding to excite higher-order modes, while the rest continues to propagate in the fundamental mode. When the light reaches the junction of the first spherical structure 5 and the second spherical structure 6, the two optical modes first couple and then split. The light is injected into the core of the second single-mode fiber 7. Throughout this process, due to the optical path difference between the fundamental mode and the higher-order modes, the phase-matching condition is met, thereby generating an interference spectrum on the spectrometer 8. The curvature and temperature are measured by the shift in the wavelength of the interference valleys in the spectrum.

[0071] The working principle of this embodiment is as follows: Incident light enters the conical region 3 through the first single-mode fiber 2. Due to the small diameter of the conical region 3, higher-order modes are excited. Subsequently, due to the superfiber connection between the first single-mode fiber 2 and the seven-core fiber 4, the light is coupled into the seven cores of the seven-core fiber 4 with low loss. After the incident light propagates 2 cm in the seven-core fiber 4, the first spherical structure 5 acts as a beam combiner to help the incident light enter. Then, through the beam-splitting effect of the second spherical structure 6, it is coupled back to the second single-mode fiber 7 and transmitted to the spectrometer 8 to obtain the transmission spectrum. During the transmission of the incident light, the fundamental mode and the cladding mode generate an optical path difference due to the difference in refractive index, thereby generating a Mach-Zehnder interference spectrum on the spectrometer. Changes in temperature and curvature will cause changes in the effective refractive index difference between the fundamental mode and the cladding mode, resulting in a wavelength shift in the spectrum. Temperature and curvature are measured by detecting the wavelength.

[0072] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A temperature and curvature sensor based on a seven-core optical fiber, characterized in that, The sensor is composed of a broadband light source (1), a first single-mode fiber (2), a cone region (3), a seven-core fiber (4), a first spherical structure (5), a second spherical structure (6), a second single-mode fiber (7), and a spectrometer (8) connected in sequence. Among them, the first single-mode fiber (2) is the input end of the sensor. One end of the first single-mode fiber (2) is connected to the broadband light source (1) through an FC / APC fiber optic connector. The two ends of the cone region (3) are respectively connected to the other end of the first single-mode fiber (2) and one end of the seven-core fiber (4). The other end of the seven-core fiber (4) is the first spherical structure (5). The second spherical structure (6) is connected to one end of the first spherical structure (5). The other end of the second spherical structure (6) is connected to one end of the second single-mode fiber (7) which is the output end. The other end of the second single-mode fiber (7) is connected to the signal interface of the spectrometer (8) through an FC / APC fiber optic connector.

2. The temperature and curvature sensor based on a seven-core optical fiber according to claim 1, characterized in that, The first single-mode fiber (2) and the second single-mode fiber (7) are single-mode fiber G.652, single-mode fiber G.654, single-mode fiber G.655 or single-mode fiber G.

656.

3. The temperature and curvature sensor based on a seven-core optical fiber according to claim 1, characterized in that, The cone region (3) includes a tapered region, a widening region, and a cone waist; the fiber diameter in the tapered region gradually decreases, the fiber diameter in the widening region gradually increases, and the fiber diameter in the cone waist is the smallest and remains constant. The conical region (3) is made by connecting single-mode optical fiber and seven-core optical fiber through an optical fiber fusion splicer and then drawing it with a hydrogen-oxygen tapering machine. The length of the conical region (3) after tapering is in the range of 2mm-40mm.

4. The temperature and curvature sensor based on a seven-core optical fiber according to claim 1, characterized in that, The first spherical structure (5) is a quasi-spherical structure. The fusion splicer melts the optical fiber by the high-voltage discharge arc between the electrodes and then pushes it forward for splicing. The discharge position of the optical fiber end is adjusted by the fusion splicer, and the discharge intensity and time of the fusion splicer are controlled to control the magnitude and duration of the discharge energy applied to the electrodes at the end of the optical fiber, thereby realizing the adjustment of the shape and size of the quasi-spherical structure.

5. The temperature and curvature sensor based on a seven-core optical fiber according to claim 1, characterized in that, The second spherical structure (6) is also a quasi-spherical structure, and its shape and size are adjusted and controlled by the amount and number of discharges to the optical fiber.

6. The temperature and curvature sensor based on a seven-core optical fiber according to claim 1, characterized in that, The first single-mode fiber (2) is connected to a broadband light source (1), and the second single-mode fiber (7) is connected to a spectrometer (8), the resolution of which is 0.02nm.

7. A method for fabricating a temperature and curvature sensor based on a seven-core optical fiber as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Connect one end of the first single-mode fiber (2) to the broadband light source (1) through the FC / APC fiber connector. Cut the other end of the first single-mode fiber (2) and the seven-core fiber (4) flat and place them on the fiber fusion splicer for splicing. The splicing point is the first splicing point. The length of the seven-core fiber (4) is 2 cm. S2. Use a fusion splicer to fuse the other end of the seven-core optical fiber (4) into a sphere as the first spherical structure (5). Perform multiple arc discharges on the right end of the seven-core optical fiber (4). The long radius of the first spherical structure (5) is 138.9 μm and the short radius is 110 μm. The diameter and size of the first spherical structure (5) are controlled and adjusted by the discharge intensity and number of discharges of the fusion splicer. S3. The second single-mode fiber (7) is connected to the spectrometer (8) through the FC / APC fiber connector. The spectrometer (8) uses the same method as in step S2 to fuse the second spherical structure (6) at the other end of the second single-mode fiber (7). S4. On the welding machine, the first spherical structure (5) and the second spherical structure (6) are brought close together and welded together by electric discharge to obtain a peanut-shaped structure. The two spherical structures are welded together either in a concentric or eccentric manner. S5. After splicing the single-mode fiber obtained in step S1 with a seven-core fiber, place it on a hydrogen-oxygen flame taper machine, align the taper machine with the first splice point, and when tapering, the flame scanning range coverage point passes through the taper to obtain the sensor.

8. The preparation method according to claim 7, characterized in that, In step S2, when the fusion splicer fuses one end of the seven-core optical fiber (4) into a sphere, it adopts manual fusion splicing mode, with a discharge intensity range of 130-150 and a discharge time of 750-950ms.

9. The preparation method according to claim 7, characterized in that, At 1 Pa and 25 °C, the flow rates of oxygen and hydrogen on the tapered machine are 8.0 mL / min and 110 mL / min, respectively. The flame scanning speed and clamping speed of the tapering machine are 2.5 mm / s and 0.08 mm / s, respectively, and the flame scanning length is 2 mm. The waist diameter of the tapered fiber is controlled by changing the tapered length. When a clear comb-like peak is observed, the tapering stops. After tapering, the expected spectrum is obtained. The length of the tapered region after tapering is 4.8789 mm.

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