Optical fiber sensor and detection system thereof

Abstract

The embodiment of the utility model discloses an optical fiber sensor and a detection system thereof. The optical fiber sensor comprises a first multimode optical fiber; a second multimode optical fiber; the first end and the second end of the bent capillary optical fiber are connected to the first multimode optical fiber and the second multimode optical fiber respectively; a bending point is arranged between the first end and the second end of the bent capillary optical fiber, the fiber core diameter of the bent capillary optical fiber at the bending point is smaller than the fiber core diameter of any other position of the bent capillary optical fiber, and the bent capillary optical fiber extends to the first end and the second end of the bent capillary optical fiber from the bending point. The diameter of the fiber core of the bent capillary optical fiber is gradually increased. The optical fiber sensor is arranged to be of a multi-section structure in which the multimode optical fiber and the capillary optical fiber are matched, and the bent capillary optical fiber is arranged to be of a bent structure, so that the optical path of the optical fiber sensor can be prolonged, an evanescent wave penetrating area is enhanced, and the coupling efficiency between a covering film on the surface of the optical fiber sensor and a light field is improved.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application relate to the technical field of optical fiber sensor, and particularly relate to an optical fiber sensor and a detection system of the optical fiber sensor. BACKGROUND

[0002] The optical fiber SPR (Surface Plasmon Resonance) sensor realizes visual monitoring of the change of refractive index of medium by depositing a metal film on a specific structural region of the optical fiber to cause strong coupling between the evanescent wave and the plasma. However, the optical fiber SPR sensor in the related art has the problems of short light field coupling path, insufficient light leakage intensity, and low sensitivity. CONTENT

[0003] The present application aims to at least solve one of the problems in the prior art or related art.

[0004] Therefore, according to a first aspect of the technical scheme of the present application, an optical fiber sensor is provided, comprising: a first multimode optical fiber; a curved capillary optical fiber, a first end of the curved capillary optical fiber being connected to one end of the first multimode optical fiber; a second multimode optical fiber, a second end of the capillary optical fiber being connected to one end of the second multimode optical fiber; wherein the curved capillary optical fiber is in a curved structure, the curved capillary optical fiber has a bending point between the first end of the curved capillary optical fiber and the second end of the curved capillary optical fiber, the diameter of the core of the curved capillary optical fiber at the bending point is smaller than the diameter of the core of the curved capillary optical fiber at any other position, and the diameter of the core of the curved capillary optical fiber gradually increases from the bending point to the first end of the curved capillary optical fiber and the second end of the curved capillary optical fiber, respectively.

[0005] In some technical schemes provided by the present application, the curved capillary optical fiber is in a U-shaped structure and has a curved portion, and the bending point is located in the curved portion, and the bending radius of the curved portion ranges from 1.3 mm to 1.7 mm.

[0006] In some technical schemes provided by the present application, the length of the first multimode optical fiber and the second multimode optical fiber ranges from 4.95 mm to 5.05 mm, and the length of the curved capillary optical fiber ranges from 3.95 mm to 4.05 mm.

[0007] In some technical schemes provided by the present application, the curved capillary optical fiber is formed by successively performing tapering and bending on a straight capillary optical fiber with a length of 2.5 mm.

[0008] In some technical schemes provided by the present application, the core of the first multimode optical fiber, the core of the curved capillary optical fiber, and the core of the second multimode optical fiber are connected in sequence, and the diameters of the cores of the first multimode optical fiber and the second multimode optical fiber are greater than the diameter of the core of the curved capillary optical fiber.

[0009] In some technical solutions provided in the application, the core of the curved capillary fiber is a hollow structure, and the core of the curved capillary fiber is filled with air.

[0010] In some technical solutions provided in the application, the outer surface of the first multimode optical fiber, the second multimode optical fiber and the curved capillary fiber is covered with a first coating film, and the first coating film is formed of gold.

[0011] In some technical solutions provided in the application, the thickness of the first coating film ranges from 45 nm to 55 nm.

[0012] In some technical solutions provided in the application, the outer surface of the first coating film is further covered with a second coating film, and the second coating film is composed of lead fluoride particles and chitosan.

[0013] The second aspect of the technical solutions of the application provides a detection system of the optical fiber sensor, which comprises the optical fiber sensor provided in the first aspect of the application, a group of to-be-measured solutions, a light source, and a spectrometer.

[0014] Compared with the prior art, the utility model at least has following beneficial effects:

[0015] The application can prolong the optical path of the optical fiber sensor, enhance the evanescent wave penetration area, improve the light leakage intensity, help to improve the coupling efficiency between the coating film on the surface of the optical fiber sensor and the light field, and improve the sensitivity of the optical fiber sensor by setting the optical fiber sensor to have a multi-section structure composed of multimode optical fibers and capillary fibers and setting the curved capillary fiber to have a curved structure. Moreover, by setting the curved capillary fiber to have a structure in which the core diameter gradually changes, additional scattering loss can be avoided. BRIEF DESCRIPTION OF DRAWINGS

[0016] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The accompanying drawings are included to provide a description of the preferred embodiments and are not intended to limit the scope of the application. Moreover, the same reference numerals in different figures represent the same or similar components. In the drawings:

[0017] Figure 1 FIG. 1 is a structural schematic diagram of an optical fiber sensor according to an embodiment of the application;

[0018] Figure 2A cross-sectional view of a curved capillary fiber according to an embodiment of the present application;

[0019] Figure 3 A cross-sectional view of a first multimode fiber according to an embodiment of the present application;

[0020] Figure 4 A structural schematic diagram of a detection system of a fiber sensor according to an embodiment of the present application;

[0021] Figure 5 A transmittance and wavelength curve obtained by a to-be-measured solution with different refractive indexes according to an embodiment of the present application;

[0022] Figure 6 Linear fitting of multiple sets of refractive indexes and wavelength values obtained by a to-be-measured solution with different refractive indexes according to an embodiment of the present application;

[0023] Figure 7 Linear fitting and polynomial fitting of multiple sets of refractive indexes and wavelength values obtained by a to-be-measured solution with different refractive indexes according to an embodiment of the present application.

[0024] wherein, Figures 1 to 7 The correspondence between the reference signs and the component names in the accompanying drawings is as follows:

[0025] 100, fiber sensor, 110, first multimode fiber, 111, core of the first multimode fiber, 120, curved capillary fiber, 121, curved portion, 122, bending point, 123, first end of the curved capillary fiber, 124, second end of the curved capillary fiber, 125, core of the curved capillary fiber, 130, second multimode fiber, 131, core of the second multimode fiber, 140, first coating film, 150, second coating film, 200, detection system of the fiber sensor, 210, to-be-measured solution, 220, light source, 230, spectrometer, 240, remote terminal. DETAILED DESCRIPTION

[0026] In order to better understand the above technical solutions, the technical solutions of the embodiments of the present application will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific features in the embodiments of the present application and the embodiments are detailed descriptions of the technical solutions of the embodiments of the present application, and are not limitations of the technical solutions of the present application. In the case of no conflict, the technical features in the embodiments of the present application and the embodiments can be combined with each other.

[0027] The following refers to Figures 1 to 7 The fiber sensor 100 and the detection system 200 of the fiber sensor according to some embodiments of the present application are described.

[0028] In an embodiment according to the present application, as shown in Fig. 1, the present application provides a fiber sensor 100, comprising: a first multimode optical fiber 110; a bent capillary fiber 120, a first end 123 of the bent capillary fiber being connected to one end of the first multimode optical fiber 110; a second multimode optical fiber 130, a second end of the capillary fiber being connected to one end of the second multimode optical fiber 130; wherein the bent capillary fiber 120 is in a bent structure, the bent capillary fiber has a bending point 122 between the first end 123 and the second end 124 of the bent capillary fiber, at the bending point 122, the diameter of the core 125 of the bent capillary fiber is smaller than the diameter of the core at any other position of the bent capillary fiber 120, and from the bending point 122 to the first end 123 and the second end 124 of the bent capillary fiber respectively, the diameter of the core 125 of the bent capillary fiber gradually increases.

[0029] The fiber sensor 100 provided by the present application is a fiber SPR sensor, and the fiber sensor 100 is in a multi-section structure, specifically comprising a first multimode optical fiber 110, a bent capillary fiber 120 and a second multimode optical fiber 130, wherein the first multimode optical fiber 110 and the second multimode optical fiber 130 are straight multimode optical fibers, the bent capillary fiber 120 is a capillary fiber in a bent structure, and the two ends of the bent capillary fiber 120 are connected to the first multimode optical fiber 110 and the second multimode optical fiber 130 respectively. The bent capillary fiber 120 has a first end and a second end, the first end 123 of the bent capillary fiber is connected to one end of the first multimode optical fiber 110, and the second end 124 of the bent capillary fiber is connected to one end of the second multimode optical fiber 130.

[0030] Further, the bent capillary fiber 120 is in a bent structure, that is, the bent capillary fiber 120 has a bending region. Moreover, the core 125 of the bent capillary fiber is in a variable diameter structure, specifically, the bent capillary fiber has a bending point 122 between the first end 123 and the second end 124 of the bent capillary fiber, at the bending point 122, the diameter of the core 125 of the bent capillary fiber is smaller than the diameter of the core at any other position of the bent capillary fiber 120, that is, the diameter of the core 125 of the bent capillary fiber is the smallest at the bending point 122. Moreover, from the bending point 122 to the first end 123 and the second end of the bent capillary fiber respectively, the diameter of the core 125 of the bent capillary fiber gradually increases, the surface of the core 125 of the bent capillary fiber is smooth, without steps and diameter mutations, thus, additional scattering loss can be avoided.

[0031] In a possible embodiment, the core 131 of the first multimode optical fiber 110 and the second multimode optical fiber has a diameter of 62.5 μm, and the cladding of the first multimode optical fiber 110 and the second multimode optical fiber 130 has a diameter of 125 μm.

[0032] The application can prolong the optical path of the optical fiber sensor 100, enhance the evanescent wave penetration area, improve the light leakage intensity, help to improve the coupling efficiency between the coating on the surface of the optical fiber sensor 100 and the light field, and improve the sensitivity of the optical fiber sensor 100 by setting the optical fiber sensor 100 to adopt a multi-section structure with a combination of a multi-mode optical fiber and a capillary optical fiber, and by setting the curved capillary optical fiber 120 to a curved structure. Moreover, by setting the curved capillary optical fiber 120 to a structure with gradually changing core diameters, additional scattering loss can be avoided.

[0033] In some embodiments, optionally, as shown in Figure 1 The curved capillary optical fiber 120 is in a U-shaped structure and has a curved portion 121, and a bending point 122 is located at the curved portion 121. The bending radius of the curved portion 121 ranges from 1.3 mm to 1.7 mm.

[0034] In this embodiment, the structure of the curved capillary optical fiber 120 is further limited. The curved capillary optical fiber 120 is in a U-shaped structure, i.e., the two sides of the bending point 122 of the curved capillary optical fiber 120 are close to symmetry, and the curved capillary optical fiber 120 has a curved portion 121, and the bending point 122 is located at the curved portion 121. Specifically, the bending point 122 is the midpoint of the curved portion 121. The bending radius of the curved portion 121 ranges from 1.3 mm to 1.7 mm. Understandably, if the bending radius of the curved portion 121 is too large, it will result in insufficient optical path length of the optical fiber sensor 100, and if the bending radius of the curved portion 121 is too small, it will easily result in damage to the curved capillary optical fiber 120. Therefore, the application limits the bending radius of the curved portion 121 to the range of 1.3 mm to 1.7 mm, so as to both prolong the optical path of the optical fiber sensor 100 and avoid damage to the curved capillary optical fiber 120. In a possible embodiment, the bending radius of the curved portion 121 is 1.5 mm.

[0035] In some embodiments, optionally, the lengths of the first multi-mode optical fiber 110 and the second multi-mode optical fiber 130 range from 4.95 mm to 5.05 mm, and the length of the curved capillary optical fiber 120 ranges from 3.95 mm to 4.05 mm.

[0036] In this embodiment, the sizes of the first multi-mode optical fiber 110, the second multi-mode optical fiber 130, and the curved capillary optical fiber 120 are limited. Specifically, the lengths of the first multi-mode optical fiber 110 and the second multi-mode optical fiber 130 range from 4.95 mm to 5.05 mm, and the length of the curved capillary optical fiber 120 ranges from 3.95 mm to 4.05 mm. In a possible embodiment, the lengths of the first multi-mode optical fiber 110 and the second multi-mode optical fiber 130 are both 5 mm, and the length of the curved capillary optical fiber 120 is 4 mm.

[0037] In some embodiments, the bent capillary fiber 120 is formed by successively performing tapering and bending on a straight capillary fiber with a length of 2.5 mm.

[0038] In this embodiment, the bent capillary fiber 120 is further defined. The bent capillary fiber 120 is processed from a straight capillary fiber. Specifically, the length of the straight capillary fiber is 2.5 mm, the straight capillary fiber is first subjected to tapering treatment, the straight capillary fiber is subjected to low-power multiple discharge treatment using a fusion machine, and the straight capillary fiber is subjected to tension stretching to elongate the length of the straight capillary fiber to 4 mm. The tapered straight capillary fiber has a symmetrical taper structure with thick ends and a thin middle. Then, the tapered straight capillary fiber is subjected to bending treatment. Specifically, the tapered straight capillary fiber is placed on a ceramic constant-temperature heating rod with a temperature of 600°C, and the tapered straight capillary fiber is slowly heated by the heating rod. Since the diameter of the middle region of the tapered straight capillary fiber is small, it is more susceptible to heat softening during heating. Under the action of external bending force, the middle region with small diameter is bent, and finally the bent capillary fiber 120 is formed. The bending point 122 of the bent capillary fiber 120 is the position with the smallest diameter in the tapered straight capillary fiber.

[0039] By tapering and bending the straight capillary fiber, the local bending radius of the fiber sensor 100 can be increased, thereby effectively lengthening the optical path of the fiber sensor 100, enhancing the evanescent wave penetration region, and helping to improve the coupling efficiency between the coating on the surface of the fiber sensor 100 and the light field.

[0040] In some embodiments, as shown in FIG. 1B, the core 111 of the first multimode fiber, the core 125 of the bent capillary fiber, and the core 131 of the second multimode fiber are connected in sequence, and the diameters of the cores 111 and 131 of the first and second multimode fibers are greater than the diameter of the core 125 of the bent capillary fiber. Figure 1

[0041] ​In this embodiment, the core 125 size of the first multimode fiber 110, the second multimode fiber 130 and the bent capillary fiber is defined. The first multimode fiber 110 and the second multimode fiber 130 each have a cladding and a core, the cladding is coated on the outside of the core, and the core 111 of the first multimode fiber, the core 125 of the bent capillary fiber and the core 131 of the second multimode fiber are connected in turn. The diameters of the cores 111 and 131 of the first and second multimode fibers are greater than the diameter of the core 125 of the bent capillary fiber, so that the connection between the core 111 of the first multimode fiber and the core 125 of the bent capillary fiber, and the connection between the core 131 of the second multimode fiber and the core 125 of the bent capillary fiber each form a core mismatch region. The core mismatch region formed by the cores of different diameters will destroy the continuity of light transmission, convert part of the guided mode into cladding mode or leaky mode, enhance the coupling and interference between modes, and thus improve the sensitivity of the fiber sensor 100. Moreover, the core mismatch region is more sensitive to external environmental changes (such as temperature, strain, refractive index, etc.), and when the external parameters change, the light transmission characteristics (such as light intensity, phase, mode distribution) of the core mismatch region will change significantly, thereby amplifying the sensing signal.

[0042] In some embodiments, optionally, the core 125 of the bent capillary fiber is a hollow structure, and the core 125 of the bent capillary fiber is filled with air inside.

[0043] In this embodiment, the structure of the bent capillary fiber 120 is further defined. The cladding of the bent capillary fiber 120 surrounds the core 125 of the bent capillary fiber to form a tubular structure, the core is located inside the tubular structure formed by the cladding, and the core has a spacing with the cladding, i.e. the diameter of the core is smaller than the diameter of the cladding. The core 125 of the bent capillary fiber is a hollow structure, and the core 125 of the bent capillary fiber is filled with air inside, i.e. the propagation medium of light is air. Compared with other types of optical fibers, the bent capillary fiber 120 with this structure has lower loss and is more suitable for being made into a bent structure.

[0044] In some embodiments, optionally, as shown in Figure 1 , Figure 2 and Figure 3 , the outer surfaces of the first multimode fiber 110, the second multimode fiber 130 and the bent capillary fiber 120 are covered with a first coating film 140, and the first coating film 140 is formed of gold.

[0045] In this embodiment, the structure of the optical fiber sensor 100 is further defined. The surfaces of the first multimode optical fiber 110, the second multimode optical fiber 130 and the curved capillary fiber 120 are all covered with the first coating film 140, which is formed of gold. Specifically, the optical fiber sensor 100 is loaded into a magnetron sputtering instrument and placed in a glass cover. The glass cover is pumped to a vacuum degree of 5 Pa by a vacuum pump. Two rounds of sputtering are performed under the condition that the current is set to 8 mA, and each round of sputtering lasts for 90 s. After the first round of sputtering is completed, the optical fiber sensor 100 is rotated by 180° and placed again in the glass cover of the magnetron sputtering instrument to perform the second round of sputtering, so as to ensure that the first coating film 140 is uniformly deposited on the curved portion 121 of the curved capillary fiber 120. Finally, the first coating film 140 with uniform thickness is obtained, which has good compactness and adhesion and can provide stable bottom support for subsequent other coating films.

[0046] In some embodiments, optionally, the thickness of the first coating film 140 ranges from 45 nm to 55 nm.

[0047] In this embodiment, the thickness range of the first coating film 140 is defined. Specifically, the thickness of the first coating film 140 ranges from 45 nm to 55 nm. Within this thickness range, the first coating film 140 can form efficient coupling with the surface plasmon wave excited by the incident light, produce obvious resonance absorption or reflection peak shift, and ensure the sensing sensitivity. In a possible embodiment, the thickness of the first coating film 140 is 50 nm.

[0048] In some embodiments, optionally, as shown in Figure 1 , Figure 2 and Figure 3 , the outside of the first coating film 140 is further covered with a second coating film 150, which is composed of lead fluoride particles and chitosan.

[0049] In this embodiment, the structure of the optical fiber sensor 100 is further defined. The outer part of the first coating film 140 of the optical fiber sensor 100 is further covered with a second coating film 150, which is composed of lead fluoride particles and chitosan, and the second coating film 150 is a sensitive film. Specifically, a chitosan solution is first prepared. 0.5 g of chitosan is dissolved in 50 ml of a 4% acetic acid aqueous solution to prepare a chitosan solution with a concentration of 10 mg / ml. Then, 0.5 g of white lead fluoride powder is added to 50 ml of the chitosan solution, and an equal volume of deionized water is added for dilution, and ultrasonic treatment is performed for 15 min to form a stable milky white suspension. A PSS (Poly (sodium 4-styrenesulfonate), poly (4-styrenesulfonic acid sodium)) solution with a concentration of 5 mg / ml is prepared, and the prepared optical fiber sensor 100 is immersed in the PSS solution for 2 min, then the optical fiber sensor 100 is taken out of the PSS solution, and is placed at room temperature for 10 min. Then the optical fiber sensor 100 is soaked in the chitosan solution containing lead fluoride for 30 min to ensure uniform adsorption of lead fluoride particles and chitosan on the surface of the first coating film 140. Subsequently, the optical fiber sensor 100 is taken out of the chitosan solution containing lead fluoride and placed in a light-proof drying environment for natural drying for 24 min to form a complete and uniform second coating film 150.

[0050] By using the first coating film 140 with high density and the second coating film 150 together to form a composite film layer on the outside of the first multimode optical fiber 110, the bent capillary optical fiber 120 and the second multimode optical fiber 130, a high sensitivity response to small changes in refractive index is achieved.

[0051] In one possible embodiment, the preparation process of the optical fiber sensor 100 is as follows:

[0052] (1) Preparation of the substrate of the optical fiber sensor 100:

[0053] In this application, a multimode fiber-capillary fiber-multimode fiber structure is used as the basis of the optical fiber sensor 100. First, a multimode fiber with a core diameter of 62.5 μm and a cladding diameter of 125 μm is selected, and a fiber stripping pliers is used to remove the coating layer at one end of the multimode fiber, and a dust-free mirror paper is used to dip anhydrous ethanol to thoroughly wipe off the residual polymer material, so that the cladding is completely exposed. Subsequently, a precision fiber cutting knife is used to cut the multimode fiber into two segments with a length of 5 mm, and the cutting error is controlled within ±0.05 mm.

[0054] A capillary optical fiber with a core diameter of 10 pm and a cladding diameter of 125 pm is selected, the coating layer with a length of 2.5 mm at one end of the capillary optical fiber is removed, and the same cleaning and cutting are performed. Finally, a high-precision optical fiber fusion machine is used to fuse the above two segments of the multimode optical fiber with a length of 5 mm and the capillary optical fiber with a length of 2.5 mm in sequence into one body, forming a sensing region with an initial structure of 5 mm multimode optical fiber-2.5 m capillary optical fiber-5 mm multimode optical fiber. The structure is the base of the optical fiber sensor 100, and the total length is 12.5 mm.

[0055] (2) Tapering treatment of the capillary optical fiber:

[0056] The middle capillary optical fiber segment in the base of the optical fiber sensor prepared above is used as a tapering target area, and a low-power multiple discharge treatment is performed on the capillary optical fiber segment using a fusion machine, combined with tension stretching, so that the capillary optical fiber segment with an original length of 2.5 mm is tapered to a length of about 4 mm. The whole process is completed under precise tension control. After tapering, the core diameter of the capillary optical fiber gradually transitions to form an axisymmetric tapered structure. The core surface of the tapered capillary optical fiber remains smooth without steps, avoiding additional scattering loss. After tapering, the total length of the sensing region (i.e., the base of the optical fiber sensor 100) is expanded to about 14 mm.

[0057] (3) Bending treatment of the capillary optical fiber:

[0058] After tapering, the base of the optical fiber sensor 100 is placed on a ceramic constant-temperature heating rod with a temperature of 600°C for slow heating, so that the tapered region of the capillary optical fiber is heat-softened and controlled to bend, and finally bent into a U-shaped sensing structure with a radius of 1.5 mm. The U-shaped sensing structure can effectively increase the local bending radius of the optical fiber sensor 100, lengthen the optical path, enhance the evanescent wave penetration area, and help improve the coupling efficiency between the second coating 150 and the optical field.

[0059] (4) Plating the first coating 140:

[0060] The U-shaped sensing structure is loaded into a magnetron sputtering instrument and placed in a glass cover. The vacuum degree is extracted to 5 Pa by a vacuum pump. Two rounds of sputtering are performed at a set current of 8 mA, with each round of sputtering time being 90 s. After the first round of sputtering, the U-shaped sensing structure is rotated by 180° and reloaded into the magnetron sputtering instrument for repeated sputtering to ensure uniform deposition of the first coating 140 in the U-shaped region. Finally, a first coating 140 with a thickness of about 50 nm is obtained, which has good compactness and adhesion and provides stable bottom support for the subsequent second coating 150.

[0061] (5) Fixing the second coating 150:

[0062] First, a chitosan solution is prepared. 0.5 g of chitosan is dissolved in 50 ml of 4% acetic acid aqueous solution to prepare a 10 mg / ml solution. Then, 0.5 g of lead fluoride white powder is added to 50 ml of the chitosan solution, and an equal volume of deionized water is added for dilution and mixing. The mixture is subjected to ultrasonic treatment for 15 min to form a stable milky white suspension. A PSS solution with a concentration of 5 mg / ml is prepared. The prepared U-shaped sensing structure with the first coating film 140 is immersed in the PSS solution for 2 min, and then taken out and left to stand at room temperature for 10 min. Then, the U-shaped sensing structure is immersed in the chitosan solution containing lead fluoride for 30 min to ensure uniform adsorption of the second coating film 150 on the surface of the first coating film 140. Subsequently, the U-shaped sensing structure is taken out and naturally dried in a light-proof drying environment for 24 h to form a complete and uniform second coating film 150 structure. The second coating film 150 is composed of lead fluoride particles and chitosan.

[0063] The second aspect of the technical solution of the present application proposes a fiber optic sensor detection system 200, which comprises the fiber optic sensor 100 proposed in the first aspect of the present application, a group of to-be-detected solutions including a plurality of to-be-detected solutions 210, the plurality of to-be-detected solutions 210 each having a different refractive index, and the plurality of to-be-detected solutions 210 being capable of being dropped on the curved capillary optical fiber 120 of the fiber optic sensor or at least a part of the curved capillary optical fiber 120 being capable of being immersed in the plurality of to-be-detected solutions 210. The fiber optic sensor detection system 200 further comprises a light source 220 connected to one end of the fiber optic sensor 100 and a spectrometer 230 with an input end connected to the other end of the fiber optic sensor 100 and an output end connected to a remote terminal 240.

[0064] As shown in Figure 4 The present application proposes a fiber optic sensor detection system 200 for detecting a fiber optic sensor 100. The fiber optic sensor detection system 200 comprises the fiber optic sensor 100, a group of to-be-detected solutions, a light source 220, and a spectrometer 230. When detecting the fiber optic sensor 100, one end of the fiber optic sensor 100 is connected to the light source 220, the other end is connected to the input end of the spectrometer 230, and the output end of the spectrometer 230 is connected to the remote terminal 240 to transmit the detection results to the remote terminal 240. The group of to-be-detected solutions comprises a plurality of to-be-detected solutions 210, each having a different refractive index. When detecting the fiber optic sensor 100, the plurality of to-be-detected solutions 210 can be dropped on the curved capillary optical fiber 120 of the fiber optic sensor 100, or the curved capillary optical fiber 120 of the fiber optic sensor 100 can be immersed in the plurality of to-be-detected solutions 210.

[0065] In one possible embodiment, a set of sodium chloride standard solutions (i.e., the test solution set) is prepared to test the refractive index response of the fiber optic sensor 100. This set of sodium chloride standard solutions includes multiple solutions with different refractive indices (i.e., test solutions 210), with refractive index values ​​of 1.33704, 1.34782, 1.35775, 1.36113, 1.36780, and 1.37784, respectively. During testing, solutions with different refractive indices are added dropwise to the U-shaped sensing region (i.e., the bent capillary fiber 120) using a dropper. Transmission spectra are acquired using software, and the redshift degree of the resonance trough is observed. To ensure a complete wavelength range response and high-sensitivity detection, a spectrometer 230 is used to construct the detection system. The spectrometer 230 covers a wavelength range of 400 nm to 1120 nm and possesses good light intensity stability. Figure 5 The figure shows the wavelength versus transmittance curves obtained using solutions with six different refractive indices. Figure 6 The results shown are obtained using solutions with six different refractive indices. Linear fitting was performed on the six sets of data to obtain... Figure 6 The diagonal lines shown in the figure represent six solutions with different refractive indices. In one possible embodiment, the equation obtained by linear fitting is y = A1 + B1x. Figure 7 The results shown are obtained using solutions with six different refractive indices. Linear fitting and polynomial fitting (i.e., nonlinear fitting) were then performed on the six sets of data to obtain the following results: Figure 7 The diagram shows a diagonal line and a curve. The six points in the diagram correspond to six solutions with different refractive indices. The diagonal line represents the linear fitting result, and the curve represents the polynomial fitting result. k in the diagram represents the slope of the curve formed by the polynomial fitting at a certain point. In one possible embodiment, the equation obtained by the polynomial fitting is y = A² + B²x + B³x. 2 .

[0066] The detection system 200 of the fiber optic sensor proposed in the second aspect of this application has all the beneficial effects of the fiber optic sensor 100 proposed in the first aspect of this application because it includes the fiber optic sensor 100 proposed in the first aspect of this application.

[0067] In the present application, the terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance; the term "a plurality of" refers to two or more than two, unless otherwise explicitly limited. The terms "mounting", "connecting", "connecting", "fixing" and other terms should be broadly understood, for example, "connecting" can be fixed connection, can also be detachable connection, or integrally connected; "connected" can be directly connected, or indirectly connected through an intermediate medium. For ordinary skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0068] In the description of the present application, it should be understood that the terms "upper", "lower", "left", "right", "front", "rear" and the like indicate the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or units referred to must have a particular direction, be constructed and operated in a particular orientation, therefore, it cannot be understood as a limitation on the present application.

[0069] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "specific embodiments" and the like means that the specific features, structures, materials or characteristics described in conjunction with the embodiments or examples are included in at least one embodiment or example of the present application. In the present application, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0070] The above is only the preferred embodiment of the present application, and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. An optical fiber sensor, characterized by, Comprising: a first multimode optical fiber; a curved capillary optical fiber, a first end of the curved capillary optical fiber being connected to one end of the first multimode optical fiber; a second multimode optical fiber, a second end of the curved capillary optical fiber being connected to one end of the second multimode optical fiber; wherein the curved capillary optical fiber is in a curved structure, the curved capillary optical fiber has a bending point between the first end of the curved capillary optical fiber and the second end of the curved capillary optical fiber, at the bending point, a diameter of a core of the curved capillary optical fiber is smaller than a diameter of a core of the curved capillary optical fiber at any other position of the curved capillary optical fiber, and from the bending point to the first end of the curved capillary optical fiber and the second end of the curved capillary optical fiber respectively, the diameter of the core of the curved capillary optical fiber gradually increases.

2. The optical fiber sensor according to claim 1, wherein the curved capillary optical fiber is in a U-shaped structure and has a curved portion, the bending point is located at the curved portion, and a bending radius of the curved portion ranges from 1.3 mm to 1.7 mm.

3. The optical fiber sensor according to claim 1, wherein a length of the first multimode optical fiber and the second multimode optical fiber ranges from 4.95 mm to 5.05 mm, and a length of the curved capillary optical fiber ranges from 3.95 mm to 4.05 mm.

4. The optical fiber sensor according to claim 3, wherein the curved capillary optical fiber is formed by successively performing tapering and bending on a straight capillary optical fiber with a length of 2.5 mm.

5. The optical fiber sensor according to claim 1, wherein a core of the first multimode optical fiber, a core of the curved capillary optical fiber, and a core of the second multimode optical fiber are connected in sequence, and a diameter of the core of the first multimode optical fiber and the second multimode optical fiber is greater than a diameter of the core of the curved capillary optical fiber.

6. The optical fiber sensor according to claim 5, wherein the core of the curved capillary optical fiber is in a hollow structure, and the core of the curved capillary optical fiber is filled with air.

7. The optical fiber sensor according to any one of claims 1 to 6, wherein an outer surface of the first multimode optical fiber, the second multimode optical fiber, and the curved capillary optical fiber is covered with a first coating film, and the first coating film is formed of gold.

8. The optical fiber sensor according to claim 7, wherein a thickness of the first coating film ranges from 45 nm to 55 nm.

9. The optical fiber sensor according to claim 7, wherein an outer portion of the first coating film is further covered with a second coating film, and the second coating film is composed of lead fluoride particles and chitosan.

10. A detection system for an optical fiber sensor, characterized by Comprising: the optical fiber sensor according to any one of claims 1 to 9; a group of to-be-measured solutions, comprising a plurality of to-be-measured solutions, the plurality of to-be-measured solutions respectively having different refractive indexes, and the plurality of to-be-measured solutions being capable of being dropped on the curved capillary optical fiber of the optical fiber sensor or at least a part of the curved capillary optical fiber being capable of being immersed in the plurality of to-be-measured solutions; a light source, connected to one end of the optical fiber sensor; a spectrometer having an input connected to the other end of the optical fiber sensor and an output connected to a remote terminal.

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