A solid-U-shaped liquid core cascade optical fiber evanescent wave sensor and its manufacturing method

Abstract

The invention discloses a solid-U-shaped liquid core cascade optical fiber evanescent wave sensor, comprising a linear solid optical fiber and a U-shaped liquid core optical fiber sealed at both ends, wherein the sealed ends of the U-shaped liquid core optical fiber are respectively connected to the light output ends of a solid optical fiber; the U-shaped liquid core optical fiber comprises a U-shaped liquid core optical fiber cladding and a U-shaped liquid core optical fiber core; the U-shaped liquid core optical fiber cladding is a hollow structure, and the U-shaped liquid core optical fiber core is a suspended particle liquid core material, and the suspended particle liquid core material is filled in the hollow structure of the U-shaped liquid core optical fiber cladding; the invention changes the core-cladding transmission mode followed by light inside a solid optical fiber, avoids the phenomenon of low sensor sensitivity caused by low luminous intensity on the surface of the solid optical fiber, enhances the light radiation capacity of the optical fiber surface, increases the evanescent wave attenuation coefficient of the sensor, and greatly enhances the sensitivity of the sensor.

Description

Technical Field

[0001] The present invention relates to the field of evanescent wave sensors, and in particular to a solid-U-shaped liquid core cascade optical fiber evanescent wave sensor and a manufacturing method thereof. Background Art

[0002] In order to realize online detection of gas and liquid composition and concentration, electrochemical, photoelectrochemical and fiber optic sensors have been developed. Fiber optic sensing technology is a brand-new technology that has emerged with the development of fiber optic communication. Fiber optic sensors modulate the light transmitted in the optical fiber through the measured physical quantity (such as liquid concentration, temperature, refractive index), so that the intensity (amplitude), phase, frequency or polarization state of the transmitted light changes, and then detect the modulated light signal to obtain a new type of sensor for the measured physical quantity.

[0003] Fiber evanescent wave sensors (such as surface plasmon resonance fiber biosensors, long-period fiber grating biosensors, photochemical fiber sensors, and fiber evanescent wave sensors) have become one of the most promising sensors for detecting gas and liquid composition and concentration due to their advantages of chemical corrosion resistance, electromagnetic interference resistance, long-distance transmission, and small size. Although fiber evanescent wave sensors have many advantages, they still have the bottleneck problem of low sensitivity.

[0004] In order to improve the sensitivity of fiber optic evanescent wave sensors, different sensitization methods and technologies have been invented. One of the simplest technologies is to optimize the shape of the sensing area, so "U"-shaped, "D"-shaped, "S"-shaped, conical, double-conical and spiral fiber optic sensors have been invented. On this basis, surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR) sensitization technologies are adopted. Although optimizing the shape of the sensor sensitive area and combining SPR or LSPR can further improve the sensitivity of the fiber optic sensor, the sensor sensitivity still depends on the evanescent field intensity on the fiber surface.

[0005] In the prior art, common solid quartz / plastic optical fibers have a core-cladding structure, which causes light transmission in the solid optical fiber to follow the core-cladding transmission mode. The core-cladding transmission mode limits light transmission within the solid optical fiber core, and the radiation intensity on the optical fiber surface depends only on the evanescent wave field. The evanescent field intensity of the solid optical fiber sensor is low and the transmission depth is small, resulting in low surface luminescence intensity in the sensitive area of ​​the solid optical fiber sensor and a small evanescent wave attenuation coefficient.

[0006] In addition, the light energy radiated from the surface of the sensitive area of ​​the optical fiber sensor provides an excitation source for detecting the concentration of the external analyte. The smaller the light radiated from the surface of the optical fiber sensitive area, the weaker the interaction between the analyte and the optical fiber, resulting in more light absorption on the surface of the optical fiber sensitive area and less attenuation of the light transmitted inside the optical fiber, and the smaller the sensor evanescent wave attenuation coefficient and the lower the sensitivity. Therefore, it is difficult to prepare a high-sensitivity evanescent wave optical fiber sensor using existing solid optical fibers.

[0007] U-shaped liquid core optical fiber is a new type of optical transmission product. It uses liquid material as the core and polymer material as the optical cladding and protective layer. It has the characteristics of large core diameter, large numerical aperture, wide spectral transmission range, high spectral transmission efficiency and long service life. In particular, the core cross section of this type of optical fiber is completely composed of the same material, which can avoid the coupling loss caused by the void ratio in the glass or quartz optical fiber transmission light beam when the single fiber is bundled; it can transmit hundreds of watts of light radiation without being damaged; there is no problem of increasingly serious broken wires and reduced light transmission efficiency due to repeated bending of glass or quartz optical fiber transmission light beams during use.

[0008] Compared with the straight liquid core optical fiber, the U-shaped liquid core optical fiber has stronger luminous intensity on the optical fiber surface, greater light radiation capacity on the optical fiber surface, greater evanescent wave attenuation coefficient of the sensor, and higher sensitivity.

[0009] In summary, the present invention explores a solid-U-shaped liquid core cascade optical fiber evanescent wave sensor in order to change the core-cladding transmission mode followed by light inside the solid optical fiber, avoid the phenomenon of low sensor sensitivity caused by low luminous intensity on the surface of the solid optical fiber, enhance the light radiation capacity of the optical fiber surface, increase the evanescent wave attenuation coefficient of the sensor, and thus enhance the sensitivity of the sensor. Summary of the invention

[0010] The object of the present invention is to provide a solid-U-shaped liquid core cascade optical fiber evanescent wave sensor and a manufacturing method thereof, so as to solve the technical problem of low sensitivity of the optical fiber evanescent wave sensor.

[0011] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0012] A solid-U-shaped liquid core cascade optical fiber evanescent wave sensor, characterized in that it includes a linear solid optical fiber 1 and a U-shaped liquid core optical fiber sealed at both ends, wherein the solid optical fiber 1 has a solid optical fiber core 7, and the two sealed ends of the U-shaped liquid core optical fiber are respectively connected to the light output ends of a solid optical fiber 1; the U-shaped liquid core optical fiber includes a U-shaped liquid core optical fiber cladding 9 and a U-shaped liquid core optical fiber core 10; the U-shaped liquid core optical fiber cladding 9 is a hollow structure, and the U-shaped liquid core optical fiber core 10 is a suspended particle liquid core material, and the suspended particle liquid core material is filled in the hollow structure of the U-shaped liquid core optical fiber cladding 9.

[0013] Preferably, the liquid core material of the suspended particles is a suspension of silica particles 11 doped with ethanol, the suspended particles are silica particles 11, and the silica particles 11 can scatter incident light; the ethanol is anhydrous ethanol, and the mass concentration of the silica in the ethanol is 5 to 35 g / L.

[0014] Preferably, the solid optical fiber 1 further comprises a solid optical fiber cladding 6 and a solid optical fiber protective layer 5 , wherein the solid optical fiber cladding 6 is coated on the outside of the solid optical fiber core 7 , and the solid optical fiber cladding 6 is coated on the outside of the solid optical fiber protective layer 5 .

[0015] Preferably, the refractive index n1 of the solid optical fiber core 7 is greater than the refractive index n2 of the solid optical fiber cladding 6, and the refractive index n′1 of the liquid core optical fiber core 10 is less than the refractive index n′2 of the liquid core optical fiber cladding 9. At the same time, the refractive index n1 of the solid optical fiber core 7 is greater than the refractive index n′1 of the liquid core optical fiber core 10.

[0016] Preferably, the output light intensity of the solid-U-shaped liquid core cascade optical fiber evanescent wave sensor can be described by the following formula:

[0017]

[0018] In the formula, I' out is the output light intensity of the sensing area of ​​the solid-liquid core cascaded optical fiber evanescent wave sensor, I' in is the input light intensity of the sensing area of ​​the solid-liquid core cascade fiber evanescent wave sensor, π is the pi constant, a' is the radius of the fiber, δ is the volume attenuation coefficient of the analyte, λ is the wavelength of the light source, and K' inner and K' outer are the parameters of the inner and outer surfaces of the solid-liquid core cascade fiber bending zone, L'1 is the length of the straight zone of the solid-liquid core cascade fiber evanescent wave sensor, L'2 is the length of the U-shaped bending zone of the solid-liquid core cascade fiber evanescent wave sensor, r is the bending radius of the liquid core fiber, θ′ is the incident angle of the light beam incident on the interface between the straight solid fiber core and the solid fiber cladding, n′1 is the refractive index of the liquid core fiber core, k1 and k2 are constant parameters, and C is the analyte concentration.

[0019] The sensing region of the solid-liquid core cascade optical fiber evanescent wave sensor refers to the U-shaped liquid core optical fiber region of the solid-liquid core cascade optical fiber evanescent wave sensor.

[0020] The present invention also discloses a method for manufacturing a solid-U-shaped liquid core cascade optical fiber evanescent wave sensor, using the solid-U-shaped liquid core cascade optical fiber evanescent wave sensor as described above, comprising the following steps:

[0021] Step 1, preparing a U-shaped liquid core optical fiber liquid core material; adding silica particles into anhydrous ethanol, and ultrasonically dispersing the silica ethanol mixture to obtain a U-shaped liquid core optical fiber liquid core material in which silica is uniformly dispersed;

[0022] Step 2, preparing a U-shaped liquid core optical fiber; soaking the U-shaped hollow capillary quartz optical fiber in a nitric acid solution for a preset time, drying the U-shaped hollow capillary quartz optical fiber after cleaning, injecting the liquid core material of the U-shaped liquid core optical fiber prepared in step 1 into a hollow capillary quartz tube, and then sealing the two ends of the U-shaped liquid core optical fiber filled with the liquid core material to obtain a U-shaped liquid core optical fiber;

[0023] Step 3: Connect the two ends of the U-shaped liquid core optical fiber to a solid optical fiber respectively, and then obtain a solid-U-shaped liquid core cascade optical fiber evanescent wave sensor.

[0024] Preferably, in step 1, the silicon dioxide particles are monodisperse silicon dioxide microspheres with a particle diameter of 200 to 3000 nm; and the mass concentration of silicon dioxide in ethanol is 5 to 35 g / L.

[0025] Preferably, in step 2, the outer diameter of the U-shaped hollow capillary quartz optical fiber is 300-2000 μm, the inner diameter is 200-1000 μm, the thickness of the U-shaped hollow capillary quartz optical fiber cladding (quartz) is 100-1000 μm, the length of the straight area is 5-100 mm, and the curvature of the curved area is 5-50 mm.

[0026] Preferably, in step 3, the length of the solid optical fiber is ≥3 cm, and the core diameter is 200-1000 μm.

[0027] Preferably, in step 3, the U-shaped liquid core optical fiber and the solid optical fiber are fused via an optical fiber connector.

[0028] The present invention has the following beneficial effects:

[0029] 1. The U-shaped liquid core fiber area in the solid-U-shaped liquid core cascade optical fiber evanescent wave sensor of the present invention is the sensitive area of ​​the sensor. The surface of the U-shaped liquid core fiber can generate evanescent waves and generate light radiation, providing excitation light energy for sensing external analyte information.

[0030] 2. The liquid core of the sensor sensing area of ​​the solid-U-shaped liquid core cascade optical fiber evanescent wave sensor of the present invention contains suspended particles, which causes the refraction of light in the solid optical fiber and the U-shaped liquid core optical fiber, the scattering of light by the suspended particles, and the U-shaped structure to change the transmission mode of light inside the solid optical fiber (the light transmission inside the solid optical fiber follows the core-cladding mode, resulting in low luminous intensity on the surface of the solid optical fiber). That is, the light in the U-shaped liquid core optical fiber no longer follows the core-cladding transmission mode, which enhances the light radiation capacity of the optical fiber surface, thereby increasing the sensor evanescent wave attenuation coefficient and the transmission light intensity inside the optical fiber.

[0031] 3. The solid-U-shaped liquid core cascade optical fiber evanescent wave sensor of the present invention has the advantages of high luminous intensity on the surface of the U-shaped liquid core optical fiber, large evanescent wave attenuation coefficient and high sensor sensitivity.

[0032] 4. Compared with the linear liquid core optical fiber, the U-shaped liquid core optical fiber used in the present invention has a stronger luminous intensity on the optical fiber surface, a greater optical fiber surface light radiation capacity, a greater sensor evanescent wave attenuation coefficient, and a higher sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to make the purpose, technical solution and advantages of the invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings, in which:

[0034] Figure 1 It is a schematic structural diagram of the solid-U-shaped liquid core cascade optical fiber evanescent wave sensor of the present invention.

[0035] Figure 2 The solid quartz U-shaped optical fiber structure and its optical transmission path schematic diagram of the present invention.

[0036] Figure 3 It is a schematic diagram of the solid-U-shaped liquid core cascade optical fiber evanescent wave sensor structure and its light transmission path of the present invention.

[0037] Figure 4 Surface radiation spectrum of the sensor sensitive area according to an embodiment of the present invention.

[0038] Figure 5 It is the radiation intensity of the surface of the sensitive area of ​​the sensor according to the embodiment of the present invention.

[0039] Figure 6 is the sensor sensitivity of the embodiment of the present invention (the relationship between the relative change of the sensor output light intensity and the glucose concentration),

[0040] Explanation of the reference numerals in the accompanying drawings: 1. solid optical fiber; 2. connection area; 31. first straight area; 32. second straight area; 4. bending area; 5. solid optical fiber protective layer; 6. solid optical fiber cladding; 7. solid optical fiber core; 8. UV shadowless adhesive; 9. U-shaped liquid core optical fiber cladding; 10. U-shaped liquid core optical fiber core; 11. silica particles; 12. U-shaped solid optical fiber core; 13. U-shaped solid optical fiber cladding; 14. U-shaped solid optical fiber straight area; 15. U-shaped sensing area; 16. outer surface of U-shaped solid optical fiber core; 17. inner surface of U-shaped solid optical fiber core. DETAILED DESCRIPTION

[0041] To make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0042] It should be noted that similar numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings. In the description of the present invention, it should be noted that the orientation or position relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. is based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the invention product is usually placed when used, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance. In addition, the terms "horizontal", "vertical", etc. do not mean that the components are absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted. In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0043] In order to solve the technical problem of low sensitivity of optical fiber evanescent wave sensors, the present invention discloses a solid-U-shaped liquid core cascade optical fiber evanescent wave sensor, so as to change the core-cladding transmission mode followed by light inside the solid optical fiber, avoid the phenomenon of low sensor sensitivity caused by low luminous intensity on the surface of the solid optical fiber, enhance the light radiation capacity of the optical fiber surface, increase the evanescent wave attenuation coefficient of the sensor, and thus enhance the sensitivity of the sensor.

[0044] like Figure 1 As shown, based on the above technical problems to be solved, the present invention discloses a solid-U-shaped liquid core cascade optical fiber evanescent wave sensor, comprising a linear solid optical fiber 1 and a U-shaped liquid core optical fiber sealed at both ends, wherein the sealed two ends of the U-shaped liquid core optical fiber are respectively connected to the light output ends of a solid optical fiber 1; the U-shaped liquid core optical fiber comprises a U-shaped liquid core optical fiber cladding 9 and a U-shaped liquid core optical fiber core 10; the U-shaped liquid core optical fiber cladding 9 is a hollow structure, and the U-shaped liquid core optical fiber core 10 is a suspended particle liquid core material, and the suspended particle liquid core material is filled in the hollow structure of the U-shaped liquid core optical fiber cladding 9.

[0045] Specifically, the U-shaped liquid core optical fiber includes a first straight area 31, a second straight area 31 and a curved area 4; wherein the first straight area 31 and the second straight area 31 are columnar, the curved area 4 is bent along a curve, and the bending angle is 180 degrees, the first straight area 31, the curved area 4 and the second straight area 31 are connected end to end in sequence to form a liquid core optical fiber whose overall appearance is roughly "U"-shaped; the two ends of the U-shaped liquid core optical fiber are sealed with UV shadowless glue 8; the U-shaped liquid core optical fiber and the solid optical fiber 1 are fused through an optical fiber connector, so that the two ends of the U-shaped liquid core optical fiber are firmly connected to the solid optical fiber 1.

[0046] Specifically, the solid optical fiber 1 further includes a solid optical fiber cladding 6 and a solid optical fiber protective layer 5 . The solid optical fiber cladding 6 is coated on the outside of the solid optical fiber core 7 . The solid optical fiber cladding 6 is coated on the outside of the solid optical fiber protective layer 5 .

[0047] The U-shaped liquid core fiber area in the solid-U-shaped liquid core cascade optical fiber evanescent wave sensor of the present invention is the sensing area of ​​the sensor, that is, the sensitive area of ​​the sensor. The surface of the U-shaped liquid core fiber can generate evanescent waves and generate light radiation, providing excitation light energy for sensing external analyte information. Due to the refraction of light in the solid optical fiber and the U-shaped liquid core optical fiber, the scattering of light by suspended particles, and the U-shaped structure changing the transmission mode of light inside the solid optical fiber (the light transmission inside the solid optical fiber follows the core-cladding mode, resulting in low luminous intensity on the surface of the solid optical fiber), that is, the light in the U-shaped liquid core optical fiber no longer follows the core-cladding transmission mode, the light radiation capacity of the optical fiber surface is enhanced, and then the evanescent wave attenuation coefficient of the sensor and the transmission light intensity inside the optical fiber are increased. The solid-U-shaped liquid core cascade optical fiber evanescent wave sensor of the present invention has the advantages of high luminous intensity on the surface of the U-shaped liquid core optical fiber, large evanescent wave attenuation coefficient, and high sensor sensitivity.

[0048] Preferably, the solid optical fiber 1 is a solid quartz optical fiber or a solid plastic optical fiber.

[0049] Preferably, the liquid core material of the suspended particles is a suspension of silica particles 11 doped with ethanol, the suspended particles are silica particles 11, and the silica particles 11 can scatter incident light; the ethanol is anhydrous ethanol, and the mass concentration of silica in ethanol is 5 to 35 g / L.

[0050] Preferably, the refractive index n1 of the solid optical fiber core 7 is greater than the refractive index n2 of the solid optical fiber cladding 6, and the refractive index n′1 of the liquid core optical fiber core 10 is less than the refractive index n′2 of the liquid core optical fiber cladding 9. At the same time, the refractive index n1 of the solid optical fiber core 7 is greater than the refractive index n′1 of the liquid core optical fiber core 10.

[0051] The refraction process of light in the solid-U-shaped liquid core cascade optical fiber evanescent wave sensor of the present invention is specifically as follows: since the refractive index n1 of the solid optical fiber core is greater than the refractive index n′1 of the liquid core optical fiber core and the refractive index n′2 of the liquid core optical fiber cladding is greater than the refractive index n′1 of the liquid core optical fiber core, refraction will occur when light is transmitted from the solid optical fiber to the U-shaped liquid core optical fiber interface; then the refracted light is transmitted to the U-shaped liquid core optical fiber and scattered by the SiO2 suspended particles in the optical fiber liquid core material; then the scattered light is transmitted to the interface between the U-shaped liquid core optical fiber core and cladding and will be refracted again to enter the U-shaped liquid core optical fiber cladding, and finally transmitted to the interface between the optical fiber cladding and the analyte, and radiated on the surface of the optical fiber cladding.

[0052] The light energy radiated from the optical fiber surface provides an excitation source for detecting the concentration of external analytes. The stronger the light radiated from the optical fiber surface, the stronger the interaction between the analyte and the optical fiber, resulting in more light absorption on the optical fiber surface and stronger attenuation of the light transmitted inside the optical fiber. The sensor has a larger evanescent wave attenuation coefficient and a higher sensitivity.

[0053] The present invention also discloses a method for manufacturing a solid-U-shaped liquid core cascade optical fiber evanescent wave sensor, using the solid-U-shaped liquid core cascade optical fiber evanescent wave sensor as described above, characterized in that it comprises the following steps:

[0054] Step 1, preparing a U-shaped liquid core optical fiber liquid core material; adding silica particles into anhydrous ethanol, and ultrasonically dispersing the silica ethanol mixture to obtain a U-shaped liquid core optical fiber liquid core material in which silica is uniformly dispersed;

[0055] Step 2, preparing a U-shaped liquid core optical fiber; soaking the U-shaped hollow capillary quartz optical fiber in a nitric acid solution for a preset time, drying the U-shaped hollow capillary quartz optical fiber after cleaning, injecting the liquid core material of the U-shaped liquid core optical fiber prepared in step 1 into a hollow capillary quartz tube, and then sealing the two ends of the U-shaped liquid core optical fiber filled with the liquid core material to obtain a U-shaped liquid core optical fiber;

[0056] Step 3: Connect the two ends of the U-shaped liquid core optical fiber to a solid optical fiber respectively, and then obtain a solid-U-shaped liquid core cascade optical fiber evanescent wave sensor.

[0057] In step 1, the silicon dioxide particles are monodisperse silicon dioxide microspheres, and the particle diameter thereof is 200 to 3000 nm.

[0058] In step 1, the mass concentration of silicon dioxide in ethanol is 5 to 35 g / L.

[0059] In step 1, the ultrasonic power used for ultrasonically dispersing the silicon dioxide ethanol mixture is 100-180W, and the ultrasonic dispersion is carried out in a water bath ultrasonic cleaning machine for 10-20 minutes.

[0060] In step 2, the concentration of the nitric acid solution is 2-5 mol / L, and the preset time is 20-30 minutes.

[0061] In step 2, the outer diameter of the U-shaped hollow capillary quartz optical fiber is 300-2000 μm, the inner diameter is 200-1000 μm, the cladding (quartz) thickness of the U-shaped hollow capillary quartz optical fiber is 100-1000 μm, the length of the straight area is 5-100 mm, and the curvature of the curved area is 5-50 mm.

[0062] In step 2, the cleaning includes ultrasonic cleaning and ultrapure water rinsing. The ultrasonic cleaning is performed using a water bath ultrasonic cleaning machine with an ultrasonic power of 160-200W for 5 to 10 minutes to clean the pollutants on the inner and outer surfaces of the hollow capillary quartz optical fiber. After the ultrasonic cleaning, the ultrapure water is used to rinse for 5 to 10 minutes to clean the nitric acid on the inner and outer surfaces of the hollow capillary quartz optical fiber. The drying treatment refers to the subsequent use of nitrogen to blow dry the water molecules attached to the inner and outer surfaces of the hollow capillary quartz optical fiber, and then the hollow capillary quartz optical fiber is placed in a vacuum drying oven and dried at 150 to 200° C. for 3 to 5 hours to remove the water molecules attached to the inner and outer surfaces of the hollow capillary quartz optical fiber.

[0063] Specifically, in step 2, the U-shaped liquid core optical fiber liquid core material is injected into the hollow capillary quartz tube using a syringe pump.

[0064] Specifically, in step 2, UV shadowless glue is used to seal the two ends of the U-shaped liquid core optical fiber filled with liquid core material, and then a scalpel is used to cut the two ends of the sealed U-shaped liquid core optical fiber flat, and then the fiber optic grinding paper is used to grind it smooth to obtain the U-shaped liquid core optical fiber.

[0065] In step 3, both ends of the solid optical fiber are polished smooth using optical fiber polishing paper, the length of the solid optical fiber is ≥3 cm, and the core diameter is 200-1000 μm.

[0066] In step 3, the U-shaped liquid core optical fiber and the solid optical fiber are fused through an optical fiber connector, so that both ends of the U-shaped liquid core optical fiber are firmly connected to the solid optical fiber.

[0067] The specific steps of fusion splicing are as follows: first, both ends of the solid optical fiber are polished to be smooth using optical fiber polishing paper, and then one end of the polished solid optical fiber is connected to the optical fiber connector; finally, the other ends of the two polished solid optical fibers are respectively fused to the two ends of the U-shaped liquid core optical fiber using an optical fiber fusion splicer, so as to obtain a solid-liquid core cascade optical fiber, that is, a solid-U-shaped liquid core cascade optical fiber evanescent wave sensor; in the solid-liquid core cascade optical fiber, an evanescent wave and light radiation will be generated on the surface of the U-shaped liquid core optical fiber, providing excitation light energy for sensing external analyte information, that is, the U-shaped liquid core optical fiber area in the solid-liquid core cascade optical fiber is the sensitive area of ​​the sensor.

[0068] The solid-U-shaped liquid core cascade optical fiber evanescent wave sensor and its manufacturing method disclosed in the present invention have the following technical effects:

[0069] The U-shaped liquid core fiber region in the solid-U-shaped liquid core cascade optical fiber evanescent wave sensor of the present invention is the sensitive region of the sensor, and the surface of the U-shaped liquid core fiber can generate evanescent waves and generate light radiation, providing excitation light energy for sensing external analyte information;

[0070] The liquid core of the sensor sensing area of ​​the solid-U-shaped liquid core cascade optical fiber evanescent wave sensor of the present invention contains suspended particles, which causes the refraction of light in the solid optical fiber and the U-shaped liquid core optical fiber, the scattering of light by the suspended particles, and the U-shaped structure to change the transmission mode of light inside the solid optical fiber (the light transmission inside the solid optical fiber follows the core-cladding mode, resulting in low luminous intensity on the surface of the solid optical fiber), that is, the light in the U-shaped liquid core optical fiber no longer follows the core-cladding transmission mode, thereby enhancing the light radiation capacity of the optical fiber surface, thereby increasing the sensor evanescent wave attenuation coefficient and the transmission light intensity inside the optical fiber;

[0071] The solid-U-shaped liquid core cascade optical fiber evanescent wave sensor of the present invention has the advantages of high surface luminescence intensity of the U-shaped liquid core optical fiber, large evanescent wave attenuation coefficient and high sensor sensitivity. Compared with the linear liquid core optical fiber, the U-shaped liquid core optical fiber used in the present invention has stronger surface luminescence intensity, greater optical fiber surface light radiation capacity, greater sensor evanescent wave attenuation coefficient and higher sensitivity.

[0072] On this basis, the present invention established a theoretical model of light transmission in a solid-U-shaped liquid core cascade optical fiber evanescent wave sensor and a theoretical model for measuring liquid concentration, and tested the concentrations of various solutions. The results showed that the sensitivity of the sensor of the present invention is 5 to 10 times greater than that of a solid optical fiber.

[0073] like Figure 2 As shown, the theoretical basis of the theoretical model of light transmission in the solid-U-shaped liquid core cascade optical fiber evanescent wave sensor is the working principle of the U-shaped solid optical fiber sensor.

[0074] The U-shaped solid optical fiber sensor includes a U-shaped solid optical fiber core 12 and a U-shaped solid optical fiber cladding 13, wherein the U-shaped solid optical fiber cladding 13 is coated on the outside of the U-shaped solid optical fiber core 12, and the U-shaped solid optical fiber sensor includes a straight area 14 and a U-shaped sensing area 15, wherein the U-shaped sensing area 15 is bent along a curve, and the bending angle is 180 degrees, and the straight area and the U-shaped sensing area are connected end to end in sequence, and the U-shaped sensing area is the sensing area of ​​the sensor, specifically:

[0075] like Figure 2 As shown, the light I in the solid optical fiber inAt the core-cladding interface, the light is confined in the fiber core by total reflection, and there is a weak evanescent wave on the surface of the sensor sensitive area. Therefore, the mechanism of solid fiber evanescent wave sensor to detect analyte concentration is based on the absorption of weak evanescent waves by analytes on the surface of the fiber sensing area, which in turn causes a weak attenuation of the light intensity transmitted inside the solid fiber. The analyte concentration is measured by measuring the change in the sensor output light intensity. After the light energy transmitted in the solid fiber is attenuated by the evanescent wave by the analyte, the output light intensity I out It is expressed as shown in formula (1):

[0076] I out =I in e -ξ(n)L (1)

[0077] In formula (1), I out is the output light intensity of the U-shaped solid fiber evanescent wave sensor in the sensing area, I in is the input light intensity of the U-shaped solid optical fiber evanescent wave sensor sensing area, ξ(n) is the evanescent wave attenuation coefficient of the analyte in the solid optical fiber evanescent wave sensor sensing area, and L is the length of the solid optical fiber evanescent wave sensor sensing area (L=L1+L2; L1 and L2 are the lengths of the straight area and U-shaped sensing area of ​​the U-shaped solid optical fiber sensor, respectively).

[0078] For the U-shaped solid optical fiber evanescent wave sensor, including a straight area and a U-shaped sensing area, ξ(n) follows: ξ(n) = ξ1(n) + ξ2(n); where ξ1(n) and ξ2(n) are the evanescent wave attenuation coefficients of the straight area and the U-shaped sensing area, respectively.

[0079] For the U-shaped solid fiber evanescent wave sensor, the expression of ξ1(n) is shown in equation (2):

[0080]

[0081] In formula (2), δ is the volume attenuation coefficient of the analyte; λ is the wavelength of the light source; n is the refractive index of the analyte; a is the radius of the optical fiber; n1 is the refractive index of the core; and θ is the incident angle of the light beam incident on the interface between the U-shaped solid optical fiber core and the U-shaped solid optical fiber cladding in the straight region.

[0082] For the U-shaped solid fiber evanescent wave sensor, the expression of ξ2(n) is shown in equation (3):

[0083]

[0084] In formula (3), [ξ eff (n)] outer and [ξ eff (n)] innerRepresent the evanescent wave absorption coefficients of the outer and inner surfaces of the U-shaped sensing region respectively; a is the radius of the optical fiber; n1 is the refractive index of the fiber core; then the parameter K of the outer surface of the U-shaped bent solid optical fiber core outer is a function of a, n1 and θ.

[0085] When the light beam inside the solid optical fiber is transmitted to the U-shaped sensing area, the integral of θ becomes the angles 16 and 17 on the outer surface 16 and the inner surface 17 of the U-shaped solid optical fiber core respectively. and ψ.

[0086] Then the parameter K outer The expression of is shown in formula (4):

[0087]

[0088] In formula (4), n1 is the refractive index of the fiber core; a is the radius of the fiber; h is Figure 2 The distance between point A and point B, is the integral of θ over the outer surface 16 of the U-shaped solid optical fiber core in the U-shaped sensing region, and The range is from arrive and The expression can be expressed as:

[0089]

[0090] In formula (5), r is the bending radius of the optical fiber (i.e. Figure 2 The distance between AO in the middle), h is Figure 2 The distance between point A and point B, n2 is the refractive index of the solid optical fiber cladding.

[0091] Similarly, the parameter K of the inner surface of the U-bend solid optical fiber core is inner It can be expressed as,

[0092]

[0093]

[0094] In equations (6a) and (6b), n1 is the refractive index of the fiber core; a is the radius of the fiber; and h is Figure 2 The distance between point A and point B in the figure, θ is the incident angle of the light beam incident on the interface between the U-shaped solid optical fiber core and the U-shaped solid optical fiber cladding in the straight area, ψ is the integral of θ on the inner surface 17 of the U-shaped solid optical fiber core in the U-shaped sensing area, and ψ varies from ψ1 to ψ2, and r is the bending radius of the optical fiber (i.e. Figure 2 The distance between AO in the middle), h is Figure 2 The distance between point A and point B, is the integral of θ over the outer surface 16 of the U-shaped solid optical fiber core in the U-shaped sensing region, and The range of changes from arrive

[0095] Therefore, using equations (1), (2) and (3), the output light intensity of the light intensity transmitted inside the U-shaped solid optical fiber after the evanescent wave attenuation can be further expressed as:

[0096]

[0097] In formula (7), I out is the output light intensity of the U-shaped solid fiber evanescent wave sensor in the sensing area, I in is the input light intensity of the sensing area of ​​the U-shaped solid fiber evanescent wave sensor, ξ1(n) and ξ2(n) are the evanescent wave attenuation coefficients of the straight area and the U-shaped sensing area of ​​the U-shaped solid fiber, L1 and L2 are the lengths of the straight area and the U-shaped sensing area of ​​the U-shaped solid fiber sensor, respectively. K outer is the parameter of the outer surface of the U-shaped solid optical fiber core, K inner is the parameter of the inner surface of the U-shaped solid optical fiber core, δ is the volume attenuation coefficient of the analyte, λ is the wavelength of the light source, n is the refractive index of the analyte, and r is the bending radius of the optical fiber (i.e. Figure 2 The distance between AO).

[0098] When the refractive index n of the analyte is less than the refractive index n1 of the solid fiber core (i.e., n / n1<1), the Taylor expansion can be applied to equation (7), and only the first two terms of the Taylor series can be used to further simplify it. The simplified equation (7) can be written as:

[0099]

[0100]

[0101] In formula (8a) and formula (8b), I out is the output light intensity of the U-shaped solid fiber evanescent wave sensor in the sensing area, I in is the input light intensity of the sensing area of ​​the U-shaped solid fiber evanescent wave sensor, n is the refractive index of the analyte, δ is the volume attenuation coefficient of the analyte, λ is the wavelength of the light source, θ is the incident angle of the light beam incident on the interface between the U-shaped solid fiber core in the straight area and the U-shaped solid fiber cladding, L1 and L2 are the lengths of the straight area and the U-shaped sensing area of ​​the U-shaped solid fiber sensor, respectively, π is the circumference constant, a is the radius of the fiber, n1 is the refractive index of the core, and r is the bending radius of the fiber (i.e. Figure 2 The distance between AO), K outer is the parameter of the outer surface of the U-shaped solid optical fiber core, K inneris the parameter of the inner surface of the U-shaped solid optical fiber core, and η is the sensitivity coefficient of the solid optical fiber evanescent wave sensor (including the U-shaped area and the straight area).

[0102] Formula (8) is the theoretical model of the solid evanescent wave optical fiber sensor for measuring the refractive index of external analytes.

[0103] Then further, the optical path diagram of the light beam propagating in the solid-liquid core cascade fiber is as follows Figure 3 As shown, the working principle of the solid-U-shaped liquid core cascade optical fiber evanescent wave sensor disclosed in the present invention is as follows:

[0104] exist Figure 3 In the solid-liquid core cascade optical fiber, after the light beam is transmitted to the interface of the solid optical fiber core 7 and the U-shaped liquid core optical fiber core 10 in sequence, the light beam I in is refracted into the liquid core (because the refractive index n1 of the solid fiber core is greater than the refractive index n′1 of the U-shaped liquid core fiber core), thereby changing the light transmission mode in the solid-liquid core cascade fiber. in When incident into the U-shaped liquid core optical fiber, the suspended silica (SiO2) particles in the liquid core material scatter it, further changing the light transmission path, and h increases to h′, that is, Figure 2 The distance between point A and point B becomes Figure 3 The distance between point D and point E in the middle also causes the incident angle of the light beam incident on the interface between the linear solid optical fiber core and the solid optical fiber cladding to be further reduced to θ′, and θ′ can be expressed as,

[0105]

[0106] In formula (9), n′1 is the refractive index of the U-shaped liquid core fiber core, n′2 is the refractive index of the U-shaped liquid core fiber cladding, N is the number of times the silica (SiO2) particles scatter the light, β is the scattering angle of the silica (SiO2) particles to the light; σ is the refraction angle of the light beam at the interface between the solid fiber core and the U-shaped liquid core fiber core, and can be expressed as:

[0107]

[0108] In addition, compared with the U-shaped solid core fiber, in the solid-liquid core cascade fiber, the incident angle of light incident on the inner and outer surfaces of the bending region is changed from and ψ are reduced to and ψ'; because the light beam has a refractive index at the interface between the U-shaped solid fiber core and the U-shaped liquid core fiber core, the scattering of light by silica (SiO2) particles, and the refraction of light at the interface between the U-shaped liquid core fiber core and the cladding (the refractive index n'1 of the U-shaped liquid core fiber core is less than the refractive index n'2 of its cladding). Therefore, and ψ' is expressed as,

[0109]

[0110]

[0111] In formulas (11a) and (11b), π is the circular constant, n′1 is the refractive index of the U-shaped liquid core fiber core, n′2 is the refractive index of the U-shaped liquid core fiber cladding, N is the number of times the silica (SiO2) particles scatter light, β is the scattering angle of the silica (SiO2) particles to light; σ is the refraction angle of the light beam at the interface between the solid fiber core and the U-shaped liquid core fiber core.

[0112] Combining equations (4), (6a) and (11), it can be seen that the bending zone coefficient K' of the solid-liquid core cascade fiber is inner and K' outer are respectively greater than the solid optical fiber bending zone coefficient K inner and K outer .

[0113] Therefore, the sensitivity coefficient η' of the solid-liquid core cascade fiber evanescent wave sensor (including the solid fiber area and the U-shaped liquid core area) is greater than the sensitivity coefficient η of the solid fiber evanescent wave sensor (including the U-shaped solid fiber straight area and the U-shaped sensing area), and η' increases with the increase of N and β.

[0114]

[0115] In formula (12), η' is the sensitivity coefficient of the solid-liquid core cascade fiber evanescent wave sensor (including the solid fiber area and the U-shaped liquid core area), a' is the radius of the fiber, δ is the volume attenuation coefficient of the analyte, λ is the wavelength of the light source, and K' is inner and K' outer are the parameters of the inner and outer surfaces of the solid-liquid core cascade fiber bending area, L'1 is the length of the straight area of ​​the solid-liquid core cascade fiber evanescent wave sensor, L'2 is the length of the U-shaped bending area of ​​the solid-liquid core cascade fiber evanescent wave sensor, r is the bending radius of the liquid core fiber (i.e. Figure 3 where n′1 is the refractive index of the liquid core fiber core, N is the number of times the silica (SiO2) particles scatter light, and β is the scattering angle of the silica (SiO2) particles to light.

[0116] Therefore, compared with the U-shaped solid fiber, after the light beam passes through the solid-liquid core cascade fiber, the function expression between the output and input light intensity can be expressed as,

[0117]

[0118] In formula (13), I' out is the output light intensity of the sensing area of ​​the solid-liquid core cascaded optical fiber evanescent wave sensor, I'in is the input light intensity of the sensing area of ​​the solid-liquid core cascade fiber evanescent wave sensor, π is the pi constant, a' is the radius of the fiber, δ is the volume attenuation coefficient of the analyte, λ is the wavelength of the light source, and K' inner and K' outer are the parameters of the inner and outer surfaces of the solid-liquid core cascade fiber bending area, L'1 is the length of the straight area of ​​the solid-liquid core cascade fiber evanescent wave sensor, L'2 is the length of the U-shaped bending area of ​​the solid-liquid core cascade fiber evanescent wave sensor, r is the bending radius of the liquid core fiber (i.e. Figure 3 The distance between CO in the middle), θ′ is the incident angle of the light beam incident on the interface between the linear solid fiber core and the solid fiber cladding, n′1 is the refractive index of the liquid core fiber core, and n is the refractive index of the analyte.

[0119] By comparing equation (8) and equation (13), it can be seen that the solid-U-shaped liquid core cascade optical fiber evanescent wave sensor increases the sensor evanescent wave attenuation coefficient, that is, increases the sensor sensitivity coefficient, which leads to a greater attenuation of the sensor output light intensity with the increase of the external refractive index n, thereby improving the sensitivity of the solid-U-shaped liquid core cascade optical fiber evanescent wave sensor.

[0120] In addition, for liquid analytes, the analyte concentration has a one-to-one linear relationship with the refractive index.

[0121] n=k1+k2C (14)

[0122] In formula (14), k1 and k2 are constant parameters, and C is the analyte concentration.

[0123] Therefore, using equations (13) and (14), the output light intensity of the solid-U-shaped liquid core cascaded optical fiber evanescent wave sensor can be further described as:

[0124]

[0125] In formula (15), I' out is the output light intensity of the sensing area of ​​the solid-liquid core cascaded optical fiber evanescent wave sensor, I' in is the input light intensity of the sensing area of ​​the solid-liquid core cascade fiber evanescent wave sensor, π is the pi constant, a' is the radius of the fiber, δ is the volume attenuation coefficient of the analyte, λ is the wavelength of the light source, and K' inner and K' outerare the parameters of the inner and outer surfaces of the solid-liquid core cascade fiber bending zone, L'1 is the length of the straight zone of the solid-liquid core cascade fiber evanescent wave sensor, L'2 is the length of the U-shaped bending zone of the solid-liquid core cascade fiber evanescent wave sensor, r is the bending radius of the liquid core fiber, θ′ is the incident angle of the light beam incident on the interface between the straight solid fiber core and the solid fiber cladding, n′1 is the refractive index of the liquid core fiber core, k1 and k2 are constant parameters, and C is the analyte concentration.

[0126] It can be seen from formula (15) that the solid-U-shaped liquid core cascade fiber evanescent wave sensor can achieve accurate measurement of analyte concentration. In addition, compared with the solid fiber evanescent wave sensor, since the liquid core fiber core refractive index n′1 is less than the liquid core fiber cladding refractive index n′2, and the solid fiber core refractive index n1 is greater than the liquid core fiber core refractive index n′1, the SiO2 dopant is used to generate light scattering, thereby changing the core-cladding transmission mode followed by the light beam in the solid fiber, increasing the evanescent wave attenuation coefficient in the sensor sensitive area, that is, the sensor sensitivity coefficient, thereby improving the sensor sensitivity.

[0127] Example

[0128] Firstly, monodisperse silica particles with a particle size of 1000 nm are added to anhydrous ethanol to prepare a silica-ethanol mixed solution with a silica mass concentration of 25 g / L, and the silica-ethanol mixed solution is ultrasonically dispersed for 10 minutes using a water bath ultrasonic cleaner with an ultrasonic power of 160 W to obtain a U-shaped liquid core optical fiber liquid core material with uniformly dispersed silica.

[0129] Secondly, a U-shaped hollow capillary quartz optical fiber with an outer diameter of 900 μm, an inner diameter of 500 μm, a straight area length of 25 mm, and a curved area curvature of 5 mm was soaked in 3 mol / L nitric acid for 20 minutes, ultrasonically cleaned for 5 minutes in a water bath ultrasonic cleaner with an ultrasonic power of 160 W, rinsed with ultrapure water for 5 minutes, dried at 150°C for 3 hours, and taken out. After cooling to room temperature, the U-shaped liquid core optical fiber liquid core material with uniformly dispersed silica was injected into the hollow capillary quartz tube.

[0130] Then, UV shadowless glue is used to seal the two ends of the U-shaped liquid core optical fiber filled with liquid core material, and a scalpel is used to cut the two ends of the sealed U-shaped liquid core optical fiber flat, and then polished with optical fiber polishing paper to obtain a U-shaped liquid core optical fiber.

[0131] Finally, the two ends of the solid optical fiber with a straight area length of 50 cm and a core diameter of 500 μm were polished smooth with optical fiber polishing paper; then one end of the polished solid optical fiber was connected to the SM905 optical fiber connector; finally, the other ends of the two polished solid optical fibers were respectively fused with the two ends of the U-shaped liquid core optical fiber using a fiber fusion splicer to obtain a solid-U-shaped liquid core cascade optical fiber evanescent wave sensor, in which the U-shaped liquid core optical fiber is the sensitive area of ​​the sensor.

[0132] In order to compare the surface radiation spectrum, emission light intensity and response sensitivity of the sensitive area of ​​the solid-U-shaped liquid core cascade fiber evanescent wave sensor (U-shaped liquid core fiber) to grape solution, a U-shaped solid fiber evanescent wave sensor with an outer diameter of 900μm, an inner diameter of 500μm, a straight sensitive area length of 25mm, and a curved sensitive area curvature of 5mm was made. The surface radiation spectrum, emission light intensity and response sensitivity of the sensor sensitive area to grape solution are shown in Figure 2. Figure 4-Figure 6 As shown ( Figure 4-Figure 6 In the figure, the excitation light source of the solid-U-shaped liquid core cascade optical fiber evanescent wave sensor and the U-shaped solid optical fiber evanescent wave sensor is the same).

[0133] Figure 4 It shows that the quality of the surface radiation spectrum of the sensitive area of ​​the solid-U-shaped liquid-core cascaded optical fiber evanescent wave sensor is higher than the spectrum of the surface radiation of the solid U-shaped solid optical fiber with the same geometric dimensions.

[0134] Figure 5 It shows that the surface radiation intensity of the sensitive area of ​​the solid-U-shaped liquid core cascade optical fiber evanescent wave sensor is higher than the surface radiation intensity of the solid U-shaped solid optical fiber with the same geometric dimensions.

[0135] Figure 6 The results show that the response sensitivity of the solid-U-shaped liquid core cascade fiber evanescent wave sensor to glucose concentration is stronger than that of the solid U-shaped solid fiber evanescent wave sensor to glucose concentration under the same geometric dimensions, and is 6.6 times that of the evanescent wave sensor to glucose concentration. Figure 6 In the figure, the relative change in the sensor output light intensity = 100% × (Iout,c-Iout,0) / Iout,0, where Iout,c and Iout,0 represent the output light intensity of the sensor when the glucose concentration is c and the glucose concentration is 0, respectively.

[0136] The following conclusions can be drawn from this embodiment: the solid-U-shaped liquid core cascade optical fiber evanescent wave sensor disclosed in the present invention changes the transmission mode of light inside the solid optical fiber. The light transmission inside the solid optical fiber follows the core-cladding mode, resulting in low luminous intensity on the surface of the solid optical fiber, that is, the light in the U-shaped liquid core optical fiber no longer follows the core-cladding transmission mode; the light radiation capacity of the optical fiber surface is enhanced, the evanescent wave attenuation coefficient of the sensor is increased, and the sensor sensitivity is higher.

[0137] It can be understood that the present invention is described by some embodiments, and those skilled in the art are aware that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the present invention. Under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the present invention. The embodiments described in the present invention are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention claimed for protection, but only represents the selected embodiments of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all other embodiments obtained by ordinary technicians in the field without creative work based on the embodiments in the present invention belong to the scope of protection of the present invention.

Claims

1. A solid-U-shaped liquid core cascade optical fiber evanescent wave sensor, characterized in that: The invention comprises a straight solid optical fiber (1) and a U-shaped liquid core optical fiber with sealed ends. The solid optical fiber (1) has a solid optical fiber core (7). The sealed ends of the U-shaped liquid core optical fiber are respectively connected to the light output ends of a solid optical fiber (1). The U-shaped liquid core optical fiber comprises a U-shaped liquid core optical fiber cladding (9) and a U-shaped liquid core optical fiber core (10). The U-shaped liquid core optical fiber cladding (9) is a hollow structure. The U-shaped liquid core optical fiber core (10) is a suspended particle liquid core material. The suspended particle liquid core material is filled in the hollow structure of the U-shaped liquid core optical fiber cladding (9). The suspended particle liquid core material is a suspension of silica particles (11) doped with ethanol; the suspended particles are silica particles (11); the silica particles (11) are capable of scattering incident light; the ethanol is anhydrous ethanol; and the mass concentration of the silica in the ethanol is 5 to 35 g / L.

2. A solid-U-shaped liquid core cascade optical fiber evanescent wave sensor according to claim 1, characterized in that: The solid optical fiber (1) further comprises a solid optical fiber cladding (6) and a solid optical fiber protective layer (5), wherein the solid optical fiber cladding (6) is coated on the outside of the solid optical fiber core (7), and the solid optical fiber protective layer (5) is coated on the outside of the solid optical fiber cladding (6).

3. A solid-U-shaped liquid core cascade optical fiber evanescent wave sensor according to claim 2, characterized in that: The refractive index n1 of the solid optical fiber core (7) is greater than the refractive index n2 of the solid optical fiber cladding (6), and the refractive index n′1 of the liquid core optical fiber core (10) is less than the refractive index n′2 of the liquid core optical fiber cladding (9). At the same time, the refractive index n1 of the solid optical fiber core (7) is greater than the refractive index n′1 of the liquid core optical fiber core (10).

4. The solid-U-shaped liquid core cascade optical fiber evanescent wave sensor according to claim 1, characterized in that: The output light intensity of the solid-U-shaped liquid core cascade optical fiber evanescent wave sensor is described by the following formula: In the formula, I' out is the output light intensity of the sensing area of ​​the solid-liquid core cascaded optical fiber evanescent wave sensor, I' in is the input light intensity of the sensing area of ​​the solid-liquid core cascade fiber evanescent wave sensor, π is the pi constant, a' is the radius of the fiber, δ is the volume attenuation coefficient of the analyte, λ is the wavelength of the light source, and K' inner and K' outer are the parameters of the inner and outer surfaces of the solid-liquid core cascade fiber bending zone, L'1 is the length of the straight zone of the solid-liquid core cascade fiber evanescent wave sensor, L'2 is the length of the U-shaped bending zone of the solid-liquid core cascade fiber evanescent wave sensor, r is the bending radius of the liquid core fiber, θ′ is the incident angle of the light beam incident on the interface between the straight solid fiber core and the solid fiber cladding, n′1 is the refractive index of the liquid core fiber core, k1 and k2 are constant parameters, and C is the analyte concentration.

5. A method for manufacturing a solid-U-shaped liquid core cascade optical fiber evanescent wave sensor, using a solid-U-shaped liquid core cascade optical fiber evanescent wave sensor as claimed in claim 1, characterized in that: The following steps are involved: Step 1, preparing a U-shaped liquid core optical fiber liquid core material; adding silica particles into anhydrous ethanol, and ultrasonically dispersing the silica ethanol mixture to obtain a U-shaped liquid core optical fiber liquid core material in which silica is uniformly dispersed; Step 2, preparing a U-shaped liquid core optical fiber; soaking the U-shaped hollow capillary quartz optical fiber in a nitric acid solution for a preset time, drying the U-shaped hollow capillary quartz optical fiber after cleaning, injecting the liquid core material of the U-shaped liquid core optical fiber prepared in step 1 into a hollow capillary quartz tube, and then sealing the two ends of the U-shaped liquid core optical fiber filled with the liquid core material to obtain a U-shaped liquid core optical fiber; Step 3: Connect the two ends of the U-shaped liquid core optical fiber to a solid optical fiber respectively, and then obtain a solid-U-shaped liquid core cascade optical fiber evanescent wave sensor.

6. The method for manufacturing a solid-U-shaped liquid core cascade optical fiber evanescent wave sensor according to claim 5, characterized in that: In step 1, the silicon dioxide particles are monodisperse silicon dioxide microspheres with a particle diameter of 200 to 3000 nm; the mass concentration of silicon dioxide in ethanol is 5 to 35 g / L.

7. The method for manufacturing a solid-U-shaped liquid core cascade optical fiber evanescent wave sensor according to claim 5, characterized in that: In step 2, the outer diameter of the U-shaped hollow capillary quartz optical fiber is 300-2000 μm, the inner diameter is 200-1000 μm, the quartz thickness of the U-shaped hollow capillary quartz optical fiber is 100-1000 μm, the length of the straight area is 5-100 mm, and the curvature of the curved area is 5-50 mm.

8. The method for manufacturing a solid-U-shaped liquid core cascade optical fiber evanescent wave sensor according to claim 5, characterized in that: In step 3, the length of the solid optical fiber is ≥3 cm, and the core diameter is 200-1000 μm.

9. The method for manufacturing a solid-U-shaped liquid core cascade optical fiber evanescent wave sensor according to claim 5, characterized in that: In step 3, the U-shaped liquid core optical fiber and the solid optical fiber are fused through an optical fiber connector.

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